Add m-esr52 at 52.6.0

1 files changed, 2619 insertions, 0 deletions

diff --git a/gfx/layers/Layers.h b/gfx/layers/Layers.h
new file mode 100644
index 000000000..805d41d48
--- /dev/null
+++ b/gfx/layers/Layers.h
@@ -0,0 +1,2619 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef GFX_LAYERS_H
+#define GFX_LAYERS_H
+
+#include <map>
+#include <stdint.h>                     // for uint32_t, uint64_t, uint8_t
+#include <stdio.h>                      // for FILE
+#include <sys/types.h>                  // for int32_t, int64_t
+#include "FrameMetrics.h"               // for FrameMetrics
+#include "Units.h"                      // for LayerMargin, LayerPoint, ParentLayerIntRect
+#include "gfxContext.h"
+#include "gfxTypes.h"
+#include "gfxPoint.h"                   // for gfxPoint
+#include "gfxRect.h"                    // for gfxRect
+#include "gfx2DGlue.h"
+#include "mozilla/Assertions.h"         // for MOZ_ASSERT_HELPER2, etc
+#include "mozilla/DebugOnly.h"          // for DebugOnly
+#include "mozilla/EventForwards.h"      // for nsPaintEvent
+#include "mozilla/Maybe.h"              // for Maybe
+#include "mozilla/Poison.h"
+#include "mozilla/RefPtr.h"             // for already_AddRefed
+#include "mozilla/StyleAnimationValue.h" // for StyleAnimationValue, etc
+#include "mozilla/TimeStamp.h"          // for TimeStamp, TimeDuration
+#include "mozilla/UniquePtr.h"          // for UniquePtr
+#include "mozilla/gfx/BaseMargin.h"     // for BaseMargin
+#include "mozilla/gfx/BasePoint.h"      // for BasePoint
+#include "mozilla/gfx/Point.h"          // for IntSize
+#include "mozilla/gfx/TiledRegion.h"    // for TiledIntRegion
+#include "mozilla/gfx/Types.h"          // for SurfaceFormat
+#include "mozilla/gfx/UserData.h"       // for UserData, etc
+#include "mozilla/layers/LayersTypes.h"
+#include "mozilla/mozalloc.h"           // for operator delete, etc
+#include "nsAutoPtr.h"                  // for nsAutoPtr, nsRefPtr, etc
+#include "nsCOMPtr.h"                   // for already_AddRefed
+#include "nsCSSPropertyID.h"              // for nsCSSPropertyID
+#include "nsDebug.h"                    // for NS_ASSERTION
+#include "nsISupportsImpl.h"            // for Layer::Release, etc
+#include "nsRect.h"                     // for mozilla::gfx::IntRect
+#include "nsRegion.h"                   // for nsIntRegion
+#include "nsString.h"                   // for nsCString
+#include "nsTArray.h"                   // for nsTArray
+#include "nsTArrayForwardDeclare.h"     // for InfallibleTArray
+#include "nscore.h"                     // for nsACString, nsAString
+#include "mozilla/Logging.h"                      // for PRLogModuleInfo
+#include "nsIWidget.h"                  // For plugin window configuration information structs
+#include "ImageContainer.h"
+
+class gfxContext;
+
+extern uint8_t gLayerManagerLayerBuilder;
+
+namespace mozilla {
+
+class ComputedTimingFunction;
+class FrameLayerBuilder;
+class StyleAnimationValue;
+
+namespace gl {
+class GLContext;
+} // namespace gl
+
+namespace gfx {
+class DrawTarget;
+} // namespace gfx
+
+namespace dom {
+class OverfillCallback;
+} // namespace dom
+
+namespace layers {
+
+class Animation;
+class AnimationData;
+class AsyncCanvasRenderer;
+class AsyncPanZoomController;
+class BasicLayerManager;
+class ClientLayerManager;
+class Layer;
+class LayerMetricsWrapper;
+class PaintedLayer;
+class ContainerLayer;
+class ImageLayer;
+class ColorLayer;
+class CanvasLayer;
+class ReadbackLayer;
+class ReadbackProcessor;
+class RefLayer;
+class LayerComposite;
+class ShadowableLayer;
+class ShadowLayerForwarder;
+class LayerManagerComposite;
+class SpecificLayerAttributes;
+class Compositor;
+class FrameUniformityData;
+class PersistentBufferProvider;
+
+namespace layerscope {
+class LayersPacket;
+} // namespace layerscope
+
+#define MOZ_LAYER_DECL_NAME(n, e)                              \
+  virtual const char* Name() const override { return n; }  \
+  virtual LayerType GetType() const override { return e; }
+
+// Defined in LayerUserData.h; please include that file instead.
+class LayerUserData;
+
+/*
+ * Motivation: For truly smooth animation and video playback, we need to
+ * be able to compose frames and render them on a dedicated thread (i.e.
+ * off the main thread where DOM manipulation, script execution and layout
+ * induce difficult-to-bound latency). This requires Gecko to construct
+ * some kind of persistent scene structure (graph or tree) that can be
+ * safely transmitted across threads. We have other scenarios (e.g. mobile
+ * browsing) where retaining some rendered data between paints is desired
+ * for performance, so again we need a retained scene structure.
+ *
+ * Our retained scene structure is a layer tree. Each layer represents
+ * content which can be composited onto a destination surface; the root
+ * layer is usually composited into a window, and non-root layers are
+ * composited into their parent layers. Layers have attributes (e.g.
+ * opacity and clipping) that influence their compositing.
+ *
+ * We want to support a variety of layer implementations, including
+ * a simple "immediate mode" implementation that doesn't retain any
+ * rendered data between paints (i.e. uses cairo in just the way that
+ * Gecko used it before layers were introduced). But we also don't want
+ * to have bifurcated "layers"/"non-layers" rendering paths in Gecko.
+ * Therefore the layers API is carefully designed to permit maximally
+ * efficient implementation in an "immediate mode" style. See the
+ * BasicLayerManager for such an implementation.
+ */
+
+/**
+ * A LayerManager controls a tree of layers. All layers in the tree
+ * must use the same LayerManager.
+ *
+ * All modifications to a layer tree must happen inside a transaction.
+ * Only the state of the layer tree at the end of a transaction is
+ * rendered. Transactions cannot be nested
+ *
+ * Each transaction has two phases:
+ * 1) Construction: layers are created, inserted, removed and have
+ * properties set on them in this phase.
+ * BeginTransaction and BeginTransactionWithTarget start a transaction in
+ * the Construction phase.
+ * 2) Drawing: PaintedLayers are rendered into in this phase, in tree
+ * order. When the client has finished drawing into the PaintedLayers, it should
+ * call EndTransaction to complete the transaction.
+ *
+ * All layer API calls happen on the main thread.
+ *
+ * Layers are refcounted. The layer manager holds a reference to the
+ * root layer, and each container layer holds a reference to its children.
+ */
+class LayerManager {
+  NS_INLINE_DECL_REFCOUNTING(LayerManager)
+
+protected:
+  typedef mozilla::gfx::DrawTarget DrawTarget;
+  typedef mozilla::gfx::IntSize IntSize;
+  typedef mozilla::gfx::SurfaceFormat SurfaceFormat;
+
+public:
+  LayerManager()
+    : mDestroyed(false)
+    , mSnapEffectiveTransforms(true)
+    , mId(0)
+    , mInTransaction(false)
+    , mPaintedPixelCount(0)
+  {}
+
+  /**
+   * Release layers and resources held by this layer manager, and mark
+   * it as destroyed.  Should do any cleanup necessary in preparation
+   * for its widget going away.  After this call, only user data calls
+   * are valid on the layer manager.
+   */
+  virtual void Destroy()
+  {
+    mDestroyed = true;
+    mUserData.Destroy();
+    mRoot = nullptr;
+  }
+  bool IsDestroyed() { return mDestroyed; }
+
+  virtual ShadowLayerForwarder* AsShadowForwarder()
+  { return nullptr; }
+
+  virtual LayerManagerComposite* AsLayerManagerComposite()
+  { return nullptr; }
+
+  virtual ClientLayerManager* AsClientLayerManager()
+  { return nullptr; }
+
+  virtual BasicLayerManager* AsBasicLayerManager()
+  { return nullptr; }
+
+  /**
+   * Returns true if this LayerManager is owned by an nsIWidget,
+   * and is used for drawing into the widget.
+   */
+  virtual bool IsWidgetLayerManager() { return true; }
+  virtual bool IsInactiveLayerManager() { return false; }
+
+  /**
+   * Start a new transaction. Nested transactions are not allowed so
+   * there must be no transaction currently in progress.
+   * This transaction will update the state of the window from which
+   * this LayerManager was obtained.
+   */
+  virtual bool BeginTransaction() = 0;
+  /**
+   * Start a new transaction. Nested transactions are not allowed so
+   * there must be no transaction currently in progress.
+   * This transaction will render the contents of the layer tree to
+   * the given target context. The rendering will be complete when
+   * EndTransaction returns.
+   */
+  virtual bool BeginTransactionWithTarget(gfxContext* aTarget) = 0;
+
+  enum EndTransactionFlags {
+    END_DEFAULT = 0,
+    END_NO_IMMEDIATE_REDRAW = 1 << 0,  // Do not perform the drawing phase
+    END_NO_COMPOSITE = 1 << 1, // Do not composite after drawing painted layer contents.
+    END_NO_REMOTE_COMPOSITE = 1 << 2 // Do not schedule a composition with a remote Compositor, if one exists.
+  };
+
+  FrameLayerBuilder* GetLayerBuilder() {
+    return reinterpret_cast<FrameLayerBuilder*>(GetUserData(&gLayerManagerLayerBuilder));
+  }
+
+  /**
+   * Attempts to end an "empty transaction". There must have been no
+   * changes to the layer tree since the BeginTransaction().
+   * It's possible for this to fail; PaintedLayers may need to be updated
+   * due to VRAM data being lost, for example. In such cases this method
+   * returns false, and the caller must proceed with a normal layer tree
+   * update and EndTransaction.
+   */
+  virtual bool EndEmptyTransaction(EndTransactionFlags aFlags = END_DEFAULT) = 0;
+
+  /**
+   * Function called to draw the contents of each PaintedLayer.
+   * aRegionToDraw contains the region that needs to be drawn.
+   * This would normally be a subregion of the visible region.
+   * The callee must draw all of aRegionToDraw. Drawing outside
+   * aRegionToDraw will be clipped out or ignored.
+   * The callee must draw all of aRegionToDraw.
+   * This region is relative to 0,0 in the PaintedLayer.
+   *
+   * aDirtyRegion should contain the total region that is be due to be painted
+   * during the transaction, even though only aRegionToDraw should be drawn
+   * during this call. aRegionToDraw must be entirely contained within
+   * aDirtyRegion. If the total dirty region is unknown it is okay to pass a
+   * subregion of the total dirty region, e.g. just aRegionToDraw, though it
+   * may not be as efficient.
+   *
+   * aRegionToInvalidate contains a region whose contents have been
+   * changed by the layer manager and which must therefore be invalidated.
+   * For example, this could be non-empty if a retained layer internally
+   * switches from RGBA to RGB or back ... we might want to repaint it to
+   * consistently use subpixel-AA or not.
+   * This region is relative to 0,0 in the PaintedLayer.
+   * aRegionToInvalidate may contain areas that are outside
+   * aRegionToDraw; the callee must ensure that these areas are repainted
+   * in the current layer manager transaction or in a later layer
+   * manager transaction.
+   *
+   * aContext must not be used after the call has returned.
+   * We guarantee that buffered contents in the visible
+   * region are valid once drawing is complete.
+   *
+   * The origin of aContext is 0,0 in the PaintedLayer.
+   */
+  typedef void (* DrawPaintedLayerCallback)(PaintedLayer* aLayer,
+                                           gfxContext* aContext,
+                                           const nsIntRegion& aRegionToDraw,
+                                           const nsIntRegion& aDirtyRegion,
+                                           DrawRegionClip aClip,
+                                           const nsIntRegion& aRegionToInvalidate,
+                                           void* aCallbackData);
+
+  /**
+   * Finish the construction phase of the transaction, perform the
+   * drawing phase, and end the transaction.
+   * During the drawing phase, all PaintedLayers in the tree are
+   * drawn in tree order, exactly once each, except for those layers
+   * where it is known that the visible region is empty.
+   */
+  virtual void EndTransaction(DrawPaintedLayerCallback aCallback,
+                              void* aCallbackData,
+                              EndTransactionFlags aFlags = END_DEFAULT) = 0;
+
+  /**
+   * Schedule a composition with the remote Compositor, if one exists
+   * for this LayerManager. Useful in conjunction with the END_NO_REMOTE_COMPOSITE
+   * flag to EndTransaction.
+   */
+  virtual void Composite() {}
+
+  virtual bool HasShadowManagerInternal() const { return false; }
+  bool HasShadowManager() const { return HasShadowManagerInternal(); }
+  virtual void StorePluginWidgetConfigurations(const nsTArray<nsIWidget::Configuration>& aConfigurations) {}
+  bool IsSnappingEffectiveTransforms() { return mSnapEffectiveTransforms; }
+
+
+  /**
+   * Returns true if the layer manager can't render component alpha
+   * layers, and layer building should do it's best to avoid
+   * creating them.
+   */
+  virtual bool ShouldAvoidComponentAlphaLayers() { return false; }
+
+  /**
+   * Returns true if this LayerManager can properly support layers with
+   * SurfaceMode::SURFACE_COMPONENT_ALPHA. LayerManagers that can't will use
+   * transparent surfaces (and lose subpixel-AA for text).
+   */
+  virtual bool AreComponentAlphaLayersEnabled();
+
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Set the root layer. The root layer is initially null. If there is
+   * no root layer, EndTransaction won't draw anything.
+   */
+  virtual void SetRoot(Layer* aLayer) = 0;
+  /**
+   * Can be called anytime
+   */
+  Layer* GetRoot() { return mRoot; }
+
+  /**
+   * Does a breadth-first search from the root layer to find the first
+   * scrollable layer, and returns its ViewID. Note that there may be
+   * other layers in the tree which share the same ViewID.
+   * Can be called any time.
+   */
+  FrameMetrics::ViewID GetRootScrollableLayerId();
+
+  /**
+   * Returns a LayerMetricsWrapper containing the Root
+   * Content Documents layer.
+   */
+  LayerMetricsWrapper GetRootContentLayer();
+
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Called when a managee has mutated.
+   * Subclasses overriding this method must first call their
+   * superclass's impl
+   */
+#ifdef DEBUG
+  // In debug builds, we check some properties of |aLayer|.
+  virtual void Mutated(Layer* aLayer);
+#else
+  virtual void Mutated(Layer* aLayer) { }
+#endif
+
+  /**
+   * Hints that can be used during PaintedLayer creation to influence the type
+   * or properties of the layer created.
+   *
+   * NONE: No hint.
+   * SCROLLABLE: This layer may represent scrollable content.
+   */
+  enum PaintedLayerCreationHint {
+    NONE, SCROLLABLE
+  };
+
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Create a PaintedLayer for this manager's layer tree.
+   */
+  virtual already_AddRefed<PaintedLayer> CreatePaintedLayer() = 0;
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Create a PaintedLayer for this manager's layer tree, with a creation hint
+   * parameter to help optimise the type of layer created.
+   */
+  virtual already_AddRefed<PaintedLayer> CreatePaintedLayerWithHint(PaintedLayerCreationHint) {
+    return CreatePaintedLayer();
+  }
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Create a ContainerLayer for this manager's layer tree.
+   */
+  virtual already_AddRefed<ContainerLayer> CreateContainerLayer() = 0;
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Create an ImageLayer for this manager's layer tree.
+   */
+  virtual already_AddRefed<ImageLayer> CreateImageLayer() = 0;
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Create a ColorLayer for this manager's layer tree.
+   */
+  virtual already_AddRefed<ColorLayer> CreateColorLayer() = 0;
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Create a CanvasLayer for this manager's layer tree.
+   */
+  virtual already_AddRefed<CanvasLayer> CreateCanvasLayer() = 0;
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Create a ReadbackLayer for this manager's layer tree.
+   */
+  virtual already_AddRefed<ReadbackLayer> CreateReadbackLayer() { return nullptr; }
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Create a RefLayer for this manager's layer tree.
+   */
+  virtual already_AddRefed<RefLayer> CreateRefLayer() { return nullptr; }
+
+
+  /**
+   * Can be called anytime, from any thread.
+   *
+   * Creates an Image container which forwards its images to the compositor within
+   * layer transactions on the main thread or asynchronously using the ImageBridge IPDL protocol.
+   * In the case of asynchronous, If the protocol is not available, the returned ImageContainer
+   * will forward images within layer transactions.
+   */
+  static already_AddRefed<ImageContainer> CreateImageContainer(ImageContainer::Mode flag
+                                                                = ImageContainer::SYNCHRONOUS);
+
+  /**
+   * Type of layer manager his is. This is to be used sparsely in order to
+   * avoid a lot of Layers backend specific code. It should be used only when
+   * Layers backend specific functionality is necessary.
+   */
+  virtual LayersBackend GetBackendType() = 0;
+
+  /**
+   * Type of layers backend that will be used to composite this layer tree.
+   * When compositing is done remotely, then this returns the layers type
+   * of the compositor.
+   */
+  virtual LayersBackend GetCompositorBackendType() { return GetBackendType(); }
+
+  /**
+   * Creates a DrawTarget which is optimized for inter-operating with this
+   * layer manager.
+   */
+  virtual already_AddRefed<DrawTarget>
+    CreateOptimalDrawTarget(const IntSize &aSize,
+                            SurfaceFormat imageFormat);
+
+  /**
+   * Creates a DrawTarget for alpha masks which is optimized for inter-
+   * operating with this layer manager. In contrast to CreateOptimalDrawTarget,
+   * this surface is optimised for drawing alpha only and we assume that
+   * drawing the mask is fairly simple.
+   */
+  virtual already_AddRefed<DrawTarget>
+    CreateOptimalMaskDrawTarget(const IntSize &aSize);
+
+  /**
+   * Creates a DrawTarget for use with canvas which is optimized for
+   * inter-operating with this layermanager.
+   */
+  virtual already_AddRefed<mozilla::gfx::DrawTarget>
+    CreateDrawTarget(const mozilla::gfx::IntSize &aSize,
+                     mozilla::gfx::SurfaceFormat aFormat);
+
+  /**
+   * Creates a PersistentBufferProvider for use with canvas which is optimized for
+   * inter-operating with this layermanager.
+   */
+  virtual already_AddRefed<PersistentBufferProvider>
+    CreatePersistentBufferProvider(const mozilla::gfx::IntSize &aSize,
+                                   mozilla::gfx::SurfaceFormat aFormat);
+
+  virtual bool CanUseCanvasLayerForSize(const gfx::IntSize &aSize) { return true; }
+
+  /**
+   * returns the maximum texture size on this layer backend, or INT32_MAX
+   * if there is no maximum
+   */
+  virtual int32_t GetMaxTextureSize() const = 0;
+
+  /**
+   * Return the name of the layer manager's backend.
+   */
+  virtual void GetBackendName(nsAString& aName) = 0;
+
+  /**
+   * This setter can be used anytime. The user data for all keys is
+   * initially null. Ownership pases to the layer manager.
+   */
+  void SetUserData(void* aKey, LayerUserData* aData)
+  {
+    mUserData.Add(static_cast<gfx::UserDataKey*>(aKey), aData, LayerUserDataDestroy);
+  }
+  /**
+   * This can be used anytime. Ownership passes to the caller!
+   */
+  UniquePtr<LayerUserData> RemoveUserData(void* aKey);
+
+  /**
+   * This getter can be used anytime.
+   */
+  bool HasUserData(void* aKey)
+  {
+    return mUserData.Has(static_cast<gfx::UserDataKey*>(aKey));
+  }
+  /**
+   * This getter can be used anytime. Ownership is retained by the layer
+   * manager.
+   */
+  LayerUserData* GetUserData(void* aKey) const
+  {
+    return static_cast<LayerUserData*>(mUserData.Get(static_cast<gfx::UserDataKey*>(aKey)));
+  }
+
+  /**
+   * Must be called outside of a layers transaction.
+   *
+   * For the subtree rooted at |aSubtree|, this attempts to free up
+   * any free-able resources like retained buffers, but may do nothing
+   * at all.  After this call, the layer tree is left in an undefined
+   * state; the layers in |aSubtree|'s subtree may no longer have
+   * buffers with valid content and may no longer be able to draw
+   * their visible and valid regions.
+   *
+   * In general, a painting or forwarding transaction on |this| must
+   * complete on the tree before it returns to a valid state.
+   *
+   * Resource freeing begins from |aSubtree| or |mRoot| if |aSubtree|
+   * is null.  |aSubtree|'s manager must be this.
+   */
+  virtual void ClearCachedResources(Layer* aSubtree = nullptr) {}
+
+  /**
+   * Flag the next paint as the first for a document.
+   */
+  virtual void SetIsFirstPaint() {}
+
+  /**
+   * Make sure that the previous transaction has been entirely
+   * completed.
+   *
+   * Note: This may sychronously wait on a remote compositor
+   * to complete rendering.
+   */
+  virtual void FlushRendering() { }
+
+  /**
+   * Checks if we need to invalidate the OS widget to trigger
+   * painting when updating this layer manager.
+   */
+  virtual bool NeedsWidgetInvalidation() { return true; }
+
+  virtual const char* Name() const { return "???"; }
+
+  /**
+   * Dump information about this layer manager and its managed tree to
+   * aStream.
+   */
+  void Dump(std::stringstream& aStream, const char* aPrefix="",
+            bool aDumpHtml=false, bool aSorted=false);
+  /**
+   * Dump information about just this layer manager itself to aStream
+   */
+  void DumpSelf(std::stringstream& aStream, const char* aPrefix="", bool aSorted=false);
+  void Dump(bool aSorted=false);
+
+  /**
+   * Dump information about this layer manager and its managed tree to
+   * layerscope packet.
+   */
+  void Dump(layerscope::LayersPacket* aPacket);
+
+  /**
+   * Log information about this layer manager and its managed tree to
+   * the NSPR log (if enabled for "Layers").
+   */
+  void Log(const char* aPrefix="");
+  /**
+   * Log information about just this layer manager itself to the NSPR
+   * log (if enabled for "Layers").
+   */
+  void LogSelf(const char* aPrefix="");
+
+  /**
+   * Record (and return) frame-intervals and paint-times for frames which were presented
+   *   between calling StartFrameTimeRecording and StopFrameTimeRecording.
+   *
+   * - Uses a cyclic buffer and serves concurrent consumers, so if Stop is called too late
+   *     (elements were overwritten since Start), result is considered invalid and hence empty.
+   * - Buffer is capable of holding 10 seconds @ 60fps (or more if frames were less frequent).
+   *     Can be changed (up to 1 hour) via pref: toolkit.framesRecording.bufferSize.
+   * - Note: the first frame-interval may be longer than expected because last frame
+   *     might have been presented some time before calling StartFrameTimeRecording.
+   */
+
+  /**
+   * Returns a handle which represents current recording start position.
+   */
+  virtual uint32_t StartFrameTimeRecording(int32_t aBufferSize);
+
+  /**
+   *  Clears, then populates aFrameIntervals with the recorded frame timing
+   *  data. The array will be empty if data was overwritten since
+   *  aStartIndex was obtained.
+   */
+  virtual void StopFrameTimeRecording(uint32_t         aStartIndex,
+                                      nsTArray<float>& aFrameIntervals);
+
+  void RecordFrame();
+  void PostPresent();
+
+  void BeginTabSwitch();
+
+  static bool IsLogEnabled();
+  static mozilla::LogModule* GetLog();
+
+  bool IsCompositingCheap(LayersBackend aBackend)
+  {
+    // LayersBackend::LAYERS_NONE is an error state, but in that case we should try to
+    // avoid loading the compositor!
+    return LayersBackend::LAYERS_BASIC != aBackend && LayersBackend::LAYERS_NONE != aBackend;
+  }
+
+  virtual bool IsCompositingCheap() { return true; }
+
+  bool IsInTransaction() const { return mInTransaction; }
+  virtual void GetFrameUniformity(FrameUniformityData* aOutData) { }
+  virtual bool RequestOverfill(mozilla::dom::OverfillCallback* aCallback) { return true; }
+  virtual void RunOverfillCallback(const uint32_t aOverfill) { }
+
+  virtual void SetRegionToClear(const nsIntRegion& aRegion)
+  {
+    mRegionToClear = aRegion;
+  }
+
+  virtual float RequestProperty(const nsAString& property) { return -1; }
+
+  const TimeStamp& GetAnimationReadyTime() const {
+    return mAnimationReadyTime;
+  }
+
+  virtual bool AsyncPanZoomEnabled() const {
+    return false;
+  }
+
+  static void LayerUserDataDestroy(void* data);
+
+  void AddPaintedPixelCount(int32_t aCount) {
+    mPaintedPixelCount += aCount;
+  }
+
+  uint32_t GetAndClearPaintedPixelCount() {
+    uint32_t count = mPaintedPixelCount;
+    mPaintedPixelCount = 0;
+    return count;
+  }
+
+protected:
+  RefPtr<Layer> mRoot;
+  gfx::UserData mUserData;
+  bool mDestroyed;
+  bool mSnapEffectiveTransforms;
+
+  nsIntRegion mRegionToClear;
+
+  // Protected destructor, to discourage deletion outside of Release():
+  virtual ~LayerManager() {}
+
+  // Print interesting information about this into aStreamo.  Internally
+  // used to implement Dump*() and Log*().
+  virtual void PrintInfo(std::stringstream& aStream, const char* aPrefix);
+
+  // Print interesting information about this into layerscope packet.
+  // Internally used to implement Dump().
+  virtual void DumpPacket(layerscope::LayersPacket* aPacket);
+
+  uint64_t mId;
+  bool mInTransaction;
+  // The time when painting most recently finished. This is recorded so that
+  // we can time any play-pending animations from this point.
+  TimeStamp mAnimationReadyTime;
+  // The count of pixels that were painted in the current transaction.
+  uint32_t mPaintedPixelCount;
+private:
+  struct FramesTimingRecording
+  {
+    // Stores state and data for frame intervals and paint times recording.
+    // see LayerManager::StartFrameTimeRecording() at Layers.cpp for more details.
+    FramesTimingRecording()
+      : mNextIndex(0)
+      , mLatestStartIndex(0)
+      , mCurrentRunStartIndex(0)
+      , mIsPaused(true)
+    {}
+    nsTArray<float> mIntervals;
+    TimeStamp mLastFrameTime;
+    uint32_t mNextIndex;
+    uint32_t mLatestStartIndex;
+    uint32_t mCurrentRunStartIndex;
+    bool mIsPaused;
+  };
+  FramesTimingRecording mRecording;
+
+  TimeStamp mTabSwitchStart;
+
+public:
+  /*
+   * Methods to store/get/clear a "pending scroll info update" object on a
+   * per-scrollid basis. This is used for empty transactions that push over
+   * scroll position updates to the APZ code.
+   */
+  void SetPendingScrollUpdateForNextTransaction(FrameMetrics::ViewID aScrollId,
+                                                const ScrollUpdateInfo& aUpdateInfo);
+  Maybe<ScrollUpdateInfo> GetPendingScrollInfoUpdate(FrameMetrics::ViewID aScrollId);
+  void ClearPendingScrollInfoUpdate();
+private:
+  std::map<FrameMetrics::ViewID,ScrollUpdateInfo> mPendingScrollUpdates;
+};
+
+typedef InfallibleTArray<Animation> AnimationArray;
+
+struct AnimData {
+  InfallibleTArray<mozilla::StyleAnimationValue> mStartValues;
+  InfallibleTArray<mozilla::StyleAnimationValue> mEndValues;
+  InfallibleTArray<Maybe<mozilla::ComputedTimingFunction>> mFunctions;
+};
+
+/**
+ * A Layer represents anything that can be rendered onto a destination
+ * surface.
+ */
+class Layer {
+  NS_INLINE_DECL_REFCOUNTING(Layer)
+
+public:
+  // Keep these in alphabetical order
+  enum LayerType {
+    TYPE_CANVAS,
+    TYPE_COLOR,
+    TYPE_CONTAINER,
+    TYPE_IMAGE,
+    TYPE_READBACK,
+    TYPE_REF,
+    TYPE_SHADOW,
+    TYPE_PAINTED
+  };
+
+  /**
+   * Returns the LayerManager this Layer belongs to. Note that the layer
+   * manager might be in a destroyed state, at which point it's only
+   * valid to set/get user data from it.
+   */
+  LayerManager* Manager() { return mManager; }
+
+  enum {
+    /**
+     * If this is set, the caller is promising that by the end of this
+     * transaction the entire visible region (as specified by
+     * SetVisibleRegion) will be filled with opaque content.
+     */
+    CONTENT_OPAQUE = 0x01,
+    /**
+     * If this is set, the caller is notifying that the contents of this layer
+     * require per-component alpha for optimal fidelity. However, there is no
+     * guarantee that component alpha will be supported for this layer at
+     * paint time.
+     * This should never be set at the same time as CONTENT_OPAQUE.
+     */
+    CONTENT_COMPONENT_ALPHA = 0x02,
+
+    /**
+     * If this is set then one of the descendant layers of this one has
+     * CONTENT_COMPONENT_ALPHA set.
+     */
+    CONTENT_COMPONENT_ALPHA_DESCENDANT = 0x04,
+
+    /**
+     * If this is set then this layer is part of a preserve-3d group, and should
+     * be sorted with sibling layers that are also part of the same group.
+     */
+    CONTENT_EXTEND_3D_CONTEXT = 0x08,
+    /**
+     * This indicates that the transform may be changed on during an empty
+     * transaction where there is no possibility of redrawing the content, so the
+     * implementation should be ready for that.
+     */
+    CONTENT_MAY_CHANGE_TRANSFORM = 0x10,
+
+    /**
+     * Disable subpixel AA for this layer. This is used if the display isn't suited
+     * for subpixel AA like hidpi or rotated content.
+     */
+    CONTENT_DISABLE_SUBPIXEL_AA = 0x20,
+
+    /**
+     * If this is set then the layer contains content that may look objectionable
+     * if not handled as an active layer (such as text with an animated transform).
+     * This is for internal layout/FrameLayerBuilder usage only until flattening
+     * code is obsoleted. See bug 633097
+     */
+    CONTENT_DISABLE_FLATTENING = 0x40,
+
+    /**
+     * This layer is hidden if the backface of the layer is visible
+     * to user.
+     */
+    CONTENT_BACKFACE_HIDDEN = 0x80
+  };
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * This lets layout make some promises about what will be drawn into the
+   * visible region of the PaintedLayer. This enables internal quality
+   * and performance optimizations.
+   */
+  void SetContentFlags(uint32_t aFlags)
+  {
+    NS_ASSERTION((aFlags & (CONTENT_OPAQUE | CONTENT_COMPONENT_ALPHA)) !=
+                 (CONTENT_OPAQUE | CONTENT_COMPONENT_ALPHA),
+                 "Can't be opaque and require component alpha");
+    if (mContentFlags != aFlags) {
+      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) ContentFlags", this));
+      mContentFlags = aFlags;
+      Mutated();
+    }
+  }
+
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * The union of the bounds of all the display item that got flattened
+   * into this layer. This is intended to be an approximation to the
+   * size of the layer if the nearest scrollable ancestor had an infinitely
+   * large displayport. Computing this more exactly is too expensive,
+   * but this approximation is sufficient for what we need to use it for.
+   */
+  virtual void SetLayerBounds(const gfx::IntRect& aLayerBounds)
+  {
+    if (!mLayerBounds.IsEqualEdges(aLayerBounds)) {
+      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) LayerBounds", this));
+      mLayerBounds = aLayerBounds;
+      Mutated();
+    }
+  }
+
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Tell this layer which region will be visible. The visible region
+   * is a region which contains all the contents of the layer that can
+   * actually affect the rendering of the window. It can exclude areas
+   * that are covered by opaque contents of other layers, and it can
+   * exclude areas where this layer simply contains no content at all.
+   * (This can be an overapproximation to the "true" visible region.)
+   *
+   * There is no general guarantee that drawing outside the bounds of the
+   * visible region will be ignored. So if a layer draws outside the bounds
+   * of its visible region, it needs to ensure that what it draws is valid.
+   */
+  virtual void SetVisibleRegion(const LayerIntRegion& aRegion)
+  {
+    // IsEmpty is required otherwise we get invalidation glitches.
+    // See bug 1288464 for investigating why.
+    if (!mVisibleRegion.IsEqual(aRegion) || aRegion.IsEmpty()) {
+      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) VisibleRegion was %s is %s", this,
+        mVisibleRegion.ToString().get(), aRegion.ToString().get()));
+      mVisibleRegion = aRegion;
+      Mutated();
+    }
+  }
+
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Set the (sub)document metrics used to render the Layer subtree
+   * rooted at this. Note that a layer may have multiple FrameMetrics
+   * objects; calling this function will remove all of them and replace
+   * them with the provided FrameMetrics. See the documentation for
+   * SetFrameMetrics(const nsTArray<FrameMetrics>&) for more details.
+   */
+  void SetScrollMetadata(const ScrollMetadata& aScrollMetadata)
+  {
+    Manager()->ClearPendingScrollInfoUpdate();
+    if (mScrollMetadata.Length() != 1 || mScrollMetadata[0] != aScrollMetadata) {
+      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) FrameMetrics", this));
+      mScrollMetadata.ReplaceElementsAt(0, mScrollMetadata.Length(), aScrollMetadata);
+      ScrollMetadataChanged();
+      Mutated();
+    }
+  }
+
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Set the (sub)document metrics used to render the Layer subtree
+   * rooted at this. There might be multiple metrics on this layer
+   * because the layer may, for example, be contained inside multiple
+   * nested scrolling subdocuments. In general a Layer having multiple
+   * ScrollMetadata objects is conceptually equivalent to having a stack
+   * of ContainerLayers that have been flattened into this Layer.
+   * See the documentation in LayerMetricsWrapper.h for a more detailed
+   * explanation of this conceptual equivalence.
+   *
+   * Note also that there is actually a many-to-many relationship between
+   * Layers and ScrollMetadata, because multiple Layers may have identical
+   * ScrollMetadata objects. This happens when those layers belong to the
+   * same scrolling subdocument and therefore end up with the same async
+   * transform when they are scrolled by the APZ code.
+   */
+  void SetScrollMetadata(const nsTArray<ScrollMetadata>& aMetadataArray)
+  {
+    Manager()->ClearPendingScrollInfoUpdate();
+    if (mScrollMetadata != aMetadataArray) {
+      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) FrameMetrics", this));
+      mScrollMetadata = aMetadataArray;
+      ScrollMetadataChanged();
+      Mutated();
+    }
+  }
+
+  /*
+   * Compositor event handling
+   * =========================
+   * When a touch-start event (or similar) is sent to the AsyncPanZoomController,
+   * it needs to decide whether the event should be sent to the main thread.
+   * Each layer has a list of event handling regions. When the compositor needs
+   * to determine how to handle a touch event, it scans the layer tree from top
+   * to bottom in z-order (traversing children before their parents). Points
+   * outside the clip region for a layer cause that layer (and its subtree)
+   * to be ignored. If a layer has a mask layer, and that mask layer's alpha
+   * value is zero at the event point, then the layer and its subtree should
+   * be ignored.
+   * For each layer, if the point is outside its hit region, we ignore the layer
+   * and move onto the next. If the point is inside its hit region but
+   * outside the dispatch-to-content region, we can initiate a gesture without
+   * consulting the content thread. Otherwise we must dispatch the event to
+   * content.
+   * Note that if a layer or any ancestor layer has a ForceEmptyHitRegion
+   * override in GetEventRegionsOverride() then the hit-region must be treated
+   * as empty. Similarly, if there is a ForceDispatchToContent override then
+   * the dispatch-to-content region must be treated as encompassing the entire
+   * hit region, and therefore we must consult the content thread before
+   * initiating a gesture. (If both flags are set, ForceEmptyHitRegion takes
+   * priority.)
+   */
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Set the event handling region.
+   */
+  void SetEventRegions(const EventRegions& aRegions)
+  {
+    if (mEventRegions != aRegions) {
+      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) eventregions were %s, now %s", this,
+        mEventRegions.ToString().get(), aRegions.ToString().get()));
+      mEventRegions = aRegions;
+      Mutated();
+    }
+  }
+
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Set the opacity which will be applied to this layer as it
+   * is composited to the destination.
+   */
+  void SetOpacity(float aOpacity)
+  {
+    if (mOpacity != aOpacity) {
+      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) Opacity", this));
+      mOpacity = aOpacity;
+      Mutated();
+    }
+  }
+
+  void SetMixBlendMode(gfx::CompositionOp aMixBlendMode)
+  {
+    if (mMixBlendMode != aMixBlendMode) {
+      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) MixBlendMode", this));
+      mMixBlendMode = aMixBlendMode;
+      Mutated();
+    }
+  }
+
+  void SetForceIsolatedGroup(bool aForceIsolatedGroup)
+  {
+    if(mForceIsolatedGroup != aForceIsolatedGroup) {
+      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) ForceIsolatedGroup", this));
+      mForceIsolatedGroup = aForceIsolatedGroup;
+      Mutated();
+    }
+  }
+
+  bool GetForceIsolatedGroup() const
+  {
+    return mForceIsolatedGroup;
+  }
+
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Set a clip rect which will be applied to this layer as it is
+   * composited to the destination. The coordinates are relative to
+   * the parent layer (i.e. the contents of this layer
+   * are transformed before this clip rect is applied).
+   * For the root layer, the coordinates are relative to the widget,
+   * in device pixels.
+   * If aRect is null no clipping will be performed.
+   */
+  void SetClipRect(const Maybe<ParentLayerIntRect>& aRect)
+  {
+    if (mClipRect) {
+      if (!aRect) {
+        MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) ClipRect was %d,%d,%d,%d is <none>", this,
+                         mClipRect->x, mClipRect->y, mClipRect->width, mClipRect->height));
+        mClipRect.reset();
+        Mutated();
+      } else {
+        if (!aRect->IsEqualEdges(*mClipRect)) {
+          MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) ClipRect was %d,%d,%d,%d is %d,%d,%d,%d", this,
+                           mClipRect->x, mClipRect->y, mClipRect->width, mClipRect->height,
+                           aRect->x, aRect->y, aRect->width, aRect->height));
+          mClipRect = aRect;
+          Mutated();
+        }
+      }
+    } else {
+      if (aRect) {
+        MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) ClipRect was <none> is %d,%d,%d,%d", this,
+                         aRect->x, aRect->y, aRect->width, aRect->height));
+        mClipRect = aRect;
+        Mutated();
+      }
+    }
+  }
+
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Set an optional scrolled clip on the layer.
+   * The scrolled clip, if present, consists of a clip rect and an optional mask.
+   * This scrolled clip is always scrolled by all scroll frames associated with
+   * this layer. (By contrast, the scroll clips stored in ScrollMetadata are
+   * only scrolled by scroll frames above that ScrollMetadata, and the layer's
+   * mClipRect is always fixed to the layer contents (which may or may not be
+   * scrolled by some of the scroll frames associated with the layer, depending
+   * on whether the layer is fixed).)
+   */
+  void SetScrolledClip(const Maybe<LayerClip>& aScrolledClip)
+  {
+    if (mScrolledClip != aScrolledClip) {
+      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) ScrolledClip", this));
+      mScrolledClip = aScrolledClip;
+      Mutated();
+    }
+  }
+
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Set a layer to mask this layer.
+   *
+   * The mask layer should be applied using its effective transform (after it
+   * is calculated by ComputeEffectiveTransformForMaskLayer), this should use
+   * this layer's parent's transform and the mask layer's transform, but not
+   * this layer's. That is, the mask layer is specified relative to this layer's
+   * position in it's parent layer's coord space.
+   * Currently, only 2D translations are supported for the mask layer transform.
+   *
+   * Ownership of aMaskLayer passes to this.
+   * Typical use would be an ImageLayer with an alpha image used for masking.
+   * See also ContainerState::BuildMaskLayer in FrameLayerBuilder.cpp.
+   */
+  void SetMaskLayer(Layer* aMaskLayer)
+  {
+#ifdef DEBUG
+    if (aMaskLayer) {
+      bool maskIs2D = aMaskLayer->GetTransform().CanDraw2D();
+      NS_ASSERTION(maskIs2D, "Mask layer has invalid transform.");
+    }
+#endif
+
+    if (mMaskLayer != aMaskLayer) {
+      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) MaskLayer", this));
+      mMaskLayer = aMaskLayer;
+      Mutated();
+    }
+  }
+
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Add mask layers associated with LayerClips.
+   */
+  void SetAncestorMaskLayers(const nsTArray<RefPtr<Layer>>& aLayers) {
+    if (aLayers != mAncestorMaskLayers) {
+      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) AncestorMaskLayers", this));
+      mAncestorMaskLayers = aLayers;
+      Mutated();
+    }
+  }
+
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Add a mask layer associated with a LayerClip.
+   */
+  void AddAncestorMaskLayer(const RefPtr<Layer>& aLayer) {
+    mAncestorMaskLayers.AppendElement(aLayer);
+    Mutated();
+  }
+
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Tell this layer what its transform should be. The transformation
+   * is applied when compositing the layer into its parent container.
+   */
+  void SetBaseTransform(const gfx::Matrix4x4& aMatrix)
+  {
+    NS_ASSERTION(!aMatrix.IsSingular(),
+                 "Shouldn't be trying to draw with a singular matrix!");
+    mPendingTransform = nullptr;
+    if (mTransform == aMatrix) {
+      return;
+    }
+    MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) BaseTransform", this));
+    mTransform = aMatrix;
+    Mutated();
+  }
+
+  /**
+   * Can be called at any time.
+   *
+   * Like SetBaseTransform(), but can be called before the next
+   * transform (i.e. outside an open transaction).  Semantically, this
+   * method enqueues a new transform value to be set immediately after
+   * the next transaction is opened.
+   */
+  void SetBaseTransformForNextTransaction(const gfx::Matrix4x4& aMatrix)
+  {
+    mPendingTransform = new gfx::Matrix4x4(aMatrix);
+  }
+
+  void SetPostScale(float aXScale, float aYScale)
+  {
+    if (mPostXScale == aXScale && mPostYScale == aYScale) {
+      return;
+    }
+    MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) PostScale", this));
+    mPostXScale = aXScale;
+    mPostYScale = aYScale;
+    Mutated();
+  }
+
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * A layer is "fixed position" when it draws content from a content
+   * (not chrome) document, the topmost content document has a root scrollframe
+   * with a displayport, but the layer does not move when that displayport scrolls.
+   */
+  void SetIsFixedPosition(bool aFixedPosition)
+  {
+    if (mIsFixedPosition != aFixedPosition) {
+      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) IsFixedPosition", this));
+      mIsFixedPosition = aFixedPosition;
+      Mutated();
+    }
+  }
+
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * This flag is true when the transform on the layer is a perspective
+   * transform. The compositor treats perspective transforms specially
+   * for async scrolling purposes.
+   */
+  void SetTransformIsPerspective(bool aTransformIsPerspective)
+  {
+    if (mTransformIsPerspective != aTransformIsPerspective) {
+      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) TransformIsPerspective", this));
+      mTransformIsPerspective = aTransformIsPerspective;
+      Mutated();
+    }
+  }
+
+  // Call AddAnimation to add a new animation to this layer from layout code.
+  // Caller must fill in all the properties of the returned animation.
+  // A later animation overrides an earlier one.
+  Animation* AddAnimation();
+  // ClearAnimations clears animations on this layer.
+  void ClearAnimations();
+  // This is only called when the layer tree is updated. Do not call this from
+  // layout code.  To add an animation to this layer, use AddAnimation.
+  void SetAnimations(const AnimationArray& aAnimations);
+  // Go through all animations in this layer and its children and, for
+  // any animations with a null start time, update their start time such
+  // that at |aReadyTime| the animation's current time corresponds to its
+  // 'initial current time' value.
+  void StartPendingAnimations(const TimeStamp& aReadyTime);
+
+  // These are a parallel to AddAnimation and clearAnimations, except
+  // they add pending animations that apply only when the next
+  // transaction is begun.  (See also
+  // SetBaseTransformForNextTransaction.)
+  Animation* AddAnimationForNextTransaction();
+  void ClearAnimationsForNextTransaction();
+
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * If a layer represents a fixed position element, this data is stored on the
+   * layer for use by the compositor.
+   *
+   *   - |aScrollId| identifies the scroll frame that this element is fixed
+   *     with respect to.
+   *
+   *   - |aAnchor| is the point on the layer that is considered the "anchor"
+   *     point, that is, the point which remains in the same position when
+   *     compositing the layer tree with a transformation (such as when
+   *     asynchronously scrolling and zooming).
+   *
+   *   - |aSides| is the set of sides to which the element is fixed relative to.
+   *     This is used if the viewport size is changed in the compositor and
+   *     fixed position items need to shift accordingly. This value is made up
+   *     combining appropriate values from mozilla::SideBits.
+   */
+  void SetFixedPositionData(FrameMetrics::ViewID aScrollId,
+                            const LayerPoint& aAnchor,
+                            int32_t aSides)
+  {
+    if (!mFixedPositionData ||
+        mFixedPositionData->mScrollId != aScrollId ||
+        mFixedPositionData->mAnchor != aAnchor ||
+        mFixedPositionData->mSides != aSides) {
+      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) FixedPositionData", this));
+      if (!mFixedPositionData) {
+        mFixedPositionData = MakeUnique<FixedPositionData>();
+      }
+      mFixedPositionData->mScrollId = aScrollId;
+      mFixedPositionData->mAnchor = aAnchor;
+      mFixedPositionData->mSides = aSides;
+      Mutated();
+    }
+  }
+
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * If a layer is "sticky position", |aScrollId| holds the scroll identifier
+   * of the scrollable content that contains it. The difference between the two
+   * rectangles |aOuter| and |aInner| is treated as two intervals in each
+   * dimension, with the current scroll position at the origin. For each
+   * dimension, while that component of the scroll position lies within either
+   * interval, the layer should not move relative to its scrolling container.
+   */
+  void SetStickyPositionData(FrameMetrics::ViewID aScrollId, LayerRect aOuter,
+                             LayerRect aInner)
+  {
+    if (!mStickyPositionData ||
+        !mStickyPositionData->mOuter.IsEqualEdges(aOuter) ||
+        !mStickyPositionData->mInner.IsEqualEdges(aInner)) {
+      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) StickyPositionData", this));
+      if (!mStickyPositionData) {
+        mStickyPositionData = new StickyPositionData;
+      }
+      mStickyPositionData->mScrollId = aScrollId;
+      mStickyPositionData->mOuter = aOuter;
+      mStickyPositionData->mInner = aInner;
+      Mutated();
+    }
+  }
+
+  enum ScrollDirection {
+    NONE,
+    VERTICAL,
+    HORIZONTAL
+  };
+
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * If a layer is a scrollbar layer, |aScrollId| holds the scroll identifier
+   * of the scrollable content that the scrollbar is for.
+   */
+  void SetScrollbarData(FrameMetrics::ViewID aScrollId, ScrollDirection aDir, float aThumbRatio)
+  {
+    if (mScrollbarTargetId != aScrollId ||
+        mScrollbarDirection != aDir ||
+        mScrollbarThumbRatio != aThumbRatio)
+    {
+      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) ScrollbarData", this));
+      mScrollbarTargetId = aScrollId;
+      mScrollbarDirection = aDir;
+      mScrollbarThumbRatio = aThumbRatio;
+      Mutated();
+    }
+  }
+
+  // Set during construction for the container layer of scrollbar components.
+  void SetIsScrollbarContainer()
+  {
+    if (!mIsScrollbarContainer) {
+      mIsScrollbarContainer = true;
+      Mutated();
+    }
+  }
+
+  // These getters can be used anytime.
+  float GetOpacity() { return mOpacity; }
+  gfx::CompositionOp GetMixBlendMode() const { return mMixBlendMode; }
+  const Maybe<ParentLayerIntRect>& GetClipRect() const { return mClipRect; }
+  const Maybe<LayerClip>& GetScrolledClip() const { return mScrolledClip; }
+  Maybe<ParentLayerIntRect> GetScrolledClipRect() const;
+  uint32_t GetContentFlags() { return mContentFlags; }
+  const gfx::IntRect& GetLayerBounds() const { return mLayerBounds; }
+  const LayerIntRegion& GetVisibleRegion() const { return mVisibleRegion; }
+  const ScrollMetadata& GetScrollMetadata(uint32_t aIndex) const;
+  const FrameMetrics& GetFrameMetrics(uint32_t aIndex) const;
+  uint32_t GetScrollMetadataCount() const { return mScrollMetadata.Length(); }
+  const nsTArray<ScrollMetadata>& GetAllScrollMetadata() { return mScrollMetadata; }
+  bool HasScrollableFrameMetrics() const;
+  bool IsScrollInfoLayer() const;
+  const EventRegions& GetEventRegions() const { return mEventRegions; }
+  ContainerLayer* GetParent() { return mParent; }
+  Layer* GetNextSibling() {
+    if (mNextSibling) {
+      mNextSibling->CheckCanary();
+    }
+    return mNextSibling;
+  }
+  const Layer* GetNextSibling() const {
+    if (mNextSibling) {
+      mNextSibling->CheckCanary();
+    }
+    return mNextSibling;
+  }
+  Layer* GetPrevSibling() { return mPrevSibling; }
+  const Layer* GetPrevSibling() const { return mPrevSibling; }
+  virtual Layer* GetFirstChild() const { return nullptr; }
+  virtual Layer* GetLastChild() const { return nullptr; }
+  gfx::Matrix4x4 GetTransform() const;
+  // Same as GetTransform(), but returns the transform as a strongly-typed
+  // matrix. Eventually this will replace GetTransform().
+  const CSSTransformMatrix GetTransformTyped() const;
+  const gfx::Matrix4x4& GetBaseTransform() const { return mTransform; }
+  // Note: these are virtual because ContainerLayerComposite overrides them.
+  virtual float GetPostXScale() const { return mPostXScale; }
+  virtual float GetPostYScale() const { return mPostYScale; }
+  bool GetIsFixedPosition() { return mIsFixedPosition; }
+  bool GetTransformIsPerspective() const { return mTransformIsPerspective; }
+  bool GetIsStickyPosition() { return mStickyPositionData; }
+  FrameMetrics::ViewID GetFixedPositionScrollContainerId() { return mFixedPositionData ? mFixedPositionData->mScrollId : FrameMetrics::NULL_SCROLL_ID; }
+  LayerPoint GetFixedPositionAnchor() { return mFixedPositionData ? mFixedPositionData->mAnchor : LayerPoint(); }
+  int32_t GetFixedPositionSides() { return mFixedPositionData ? mFixedPositionData->mSides : eSideBitsNone; }
+  FrameMetrics::ViewID GetStickyScrollContainerId() { return mStickyPositionData->mScrollId; }
+  const LayerRect& GetStickyScrollRangeOuter() { return mStickyPositionData->mOuter; }
+  const LayerRect& GetStickyScrollRangeInner() { return mStickyPositionData->mInner; }
+  FrameMetrics::ViewID GetScrollbarTargetContainerId() { return mScrollbarTargetId; }
+  ScrollDirection GetScrollbarDirection() { return mScrollbarDirection; }
+  float GetScrollbarThumbRatio() { return mScrollbarThumbRatio; }
+  bool IsScrollbarContainer() { return mIsScrollbarContainer; }
+  Layer* GetMaskLayer() const { return mMaskLayer; }
+  void CheckCanary() const { mCanary.Check(); }
+
+  // Ancestor mask layers are associated with FrameMetrics, but for simplicity
+  // in maintaining the layer tree structure we attach them to the layer.
+  size_t GetAncestorMaskLayerCount() const {
+    return mAncestorMaskLayers.Length();
+  }
+  Layer* GetAncestorMaskLayerAt(size_t aIndex) const {
+    return mAncestorMaskLayers.ElementAt(aIndex);
+  }
+  const nsTArray<RefPtr<Layer>>& GetAllAncestorMaskLayers() const {
+    return mAncestorMaskLayers;
+  }
+
+  bool HasMaskLayers() const {
+    return GetMaskLayer() || mAncestorMaskLayers.Length() > 0;
+  }
+
+  /*
+   * Get the combined clip rect of the Layer clip and all clips on FrameMetrics.
+   * This is intended for use in Layout. The compositor needs to apply async
+   * transforms to find the combined clip.
+   */
+  Maybe<ParentLayerIntRect> GetCombinedClipRect() const;
+
+  /**
+   * Retrieve the root level visible region for |this| taking into account
+   * clipping applied to parent layers of |this| as well as subtracting
+   * visible regions of higher siblings of this layer and each ancestor.
+   *
+   * Note translation values for offsets of visible regions and accumulated
+   * aLayerOffset are integer rounded using IntPoint::Round.
+   *
+   * @param aResult - the resulting visible region of this layer.
+   * @param aLayerOffset - this layer's total offset from the root layer.
+   * @return - false if during layer tree traversal a parent or sibling
+   *  transform is found to be non-translational. This method returns early
+   *  in this case, results will not be valid. Returns true on successful
+   *  traversal.
+   */
+  bool GetVisibleRegionRelativeToRootLayer(nsIntRegion& aResult,
+                                           nsIntPoint* aLayerOffset);
+
+  // Note that all lengths in animation data are either in CSS pixels or app
+  // units and must be converted to device pixels by the compositor.
+  AnimationArray& GetAnimations() { return mAnimations; }
+  InfallibleTArray<AnimData>& GetAnimationData() { return mAnimationData; }
+
+  uint64_t GetAnimationGeneration() { return mAnimationGeneration; }
+  void SetAnimationGeneration(uint64_t aCount) { mAnimationGeneration = aCount; }
+
+  bool HasTransformAnimation() const;
+
+  /**
+   * Returns the local transform for this layer: either mTransform or,
+   * for shadow layers, GetShadowBaseTransform(), in either case with the
+   * pre- and post-scales applied.
+   */
+  gfx::Matrix4x4 GetLocalTransform();
+
+  /**
+   * Same as GetLocalTransform(), but returns a strongly-typed matrix.
+   * Eventually, this will replace GetLocalTransform().
+   */
+  const LayerToParentLayerMatrix4x4 GetLocalTransformTyped();
+
+  /**
+   * Returns the local opacity for this layer: either mOpacity or,
+   * for shadow layers, GetShadowOpacity()
+   */
+  float GetLocalOpacity();
+
+  /**
+   * DRAWING PHASE ONLY
+   *
+   * Apply pending changes to layers before drawing them, if those
+   * pending changes haven't been overridden by later changes.
+   */
+  void ApplyPendingUpdatesToSubtree();
+
+  /**
+   * DRAWING PHASE ONLY
+   *
+   * Write layer-subtype-specific attributes into aAttrs.  Used to
+   * synchronize layer attributes to their shadows'.
+   */
+  virtual void FillSpecificAttributes(SpecificLayerAttributes& aAttrs) { }
+
+  // Returns true if it's OK to save the contents of aLayer in an
+  // opaque surface (a surface without an alpha channel).
+  // If we can use a surface without an alpha channel, we should, because
+  // it will often make painting of antialiased text faster and higher
+  // quality.
+  bool CanUseOpaqueSurface();
+
+  SurfaceMode GetSurfaceMode()
+  {
+    if (CanUseOpaqueSurface())
+      return SurfaceMode::SURFACE_OPAQUE;
+    if (mContentFlags & CONTENT_COMPONENT_ALPHA)
+      return SurfaceMode::SURFACE_COMPONENT_ALPHA;
+    return SurfaceMode::SURFACE_SINGLE_CHANNEL_ALPHA;
+  }
+
+  // Returns true if this layer can be treated as opaque for visibility
+  // computation. A layer may be non-opaque for visibility even if it
+  // is not transparent, for example, if it has a mix-blend-mode.
+  bool IsOpaqueForVisibility();
+
+  /**
+   * This setter can be used anytime. The user data for all keys is
+   * initially null. Ownership pases to the layer manager.
+   */
+  void SetUserData(void* aKey, LayerUserData* aData)
+  {
+    mUserData.Add(static_cast<gfx::UserDataKey*>(aKey), aData, LayerManager::LayerUserDataDestroy);
+  }
+  /**
+   * This can be used anytime. Ownership passes to the caller!
+   */
+  UniquePtr<LayerUserData> RemoveUserData(void* aKey);
+  /**
+   * This getter can be used anytime.
+   */
+  bool HasUserData(void* aKey)
+  {
+    return mUserData.Has(static_cast<gfx::UserDataKey*>(aKey));
+  }
+  /**
+   * This getter can be used anytime. Ownership is retained by the layer
+   * manager.
+   */
+  LayerUserData* GetUserData(void* aKey) const
+  {
+    return static_cast<LayerUserData*>(mUserData.Get(static_cast<gfx::UserDataKey*>(aKey)));
+  }
+
+  /**
+   * |Disconnect()| is used by layers hooked up over IPC.  It may be
+   * called at any time, and may not be called at all.  Using an
+   * IPC-enabled layer after Destroy() (drawing etc.) results in a
+   * safe no-op; no crashy or uaf etc.
+   *
+   * XXX: this interface is essentially LayerManager::Destroy, but at
+   * Layer granularity.  It might be beneficial to unify them.
+   */
+  virtual void Disconnect() {}
+
+  /**
+   * Dynamic downcast to a PaintedLayer. Returns null if this is not
+   * a PaintedLayer.
+   */
+  virtual PaintedLayer* AsPaintedLayer() { return nullptr; }
+
+  /**
+   * Dynamic cast to a ContainerLayer. Returns null if this is not
+   * a ContainerLayer.
+   */
+  virtual ContainerLayer* AsContainerLayer() { return nullptr; }
+  virtual const ContainerLayer* AsContainerLayer() const { return nullptr; }
+
+   /**
+    * Dynamic cast to a RefLayer. Returns null if this is not a
+    * RefLayer.
+    */
+  virtual RefLayer* AsRefLayer() { return nullptr; }
+
+   /**
+    * Dynamic cast to a Color. Returns null if this is not a
+    * ColorLayer.
+    */
+  virtual ColorLayer* AsColorLayer() { return nullptr; }
+
+  /**
+   * Dynamic cast to a LayerComposite.  Return null if this is not a
+   * LayerComposite.  Can be used anytime.
+   */
+  virtual LayerComposite* AsLayerComposite() { return nullptr; }
+
+  /**
+   * Dynamic cast to a ShadowableLayer.  Return null if this is not a
+   * ShadowableLayer.  Can be used anytime.
+   */
+  virtual ShadowableLayer* AsShadowableLayer() { return nullptr; }
+
+  // These getters can be used anytime.  They return the effective
+  // values that should be used when drawing this layer to screen,
+  // accounting for this layer possibly being a shadow.
+  const Maybe<ParentLayerIntRect>& GetLocalClipRect();
+  const LayerIntRegion& GetLocalVisibleRegion();
+
+  bool Extend3DContext() {
+    return GetContentFlags() & CONTENT_EXTEND_3D_CONTEXT;
+  }
+  bool Combines3DTransformWithAncestors() {
+    return GetParent() &&
+      reinterpret_cast<Layer*>(GetParent())->Extend3DContext();
+  }
+  bool Is3DContextLeaf() {
+    return !Extend3DContext() && Combines3DTransformWithAncestors();
+  }
+  /**
+   * It is true if the user can see the back of the layer and the
+   * backface is hidden.  The compositor should skip the layer if the
+   * result is true.
+   */
+  bool IsBackfaceHidden();
+  bool IsVisible() {
+    // For containers extending 3D context, visible region
+    // is meaningless, since they are just intermediate result of
+    // content.
+    return !GetLocalVisibleRegion().IsEmpty() || Extend3DContext();
+  }
+
+  /**
+   * Return true if current layer content is opaque.
+   * It does not guarantee that layer content is always opaque.
+   */
+  virtual bool IsOpaque() { return GetContentFlags() & CONTENT_OPAQUE; }
+
+  /**
+   * Returns the product of the opacities of this layer and all ancestors up
+   * to and excluding the nearest ancestor that has UseIntermediateSurface() set.
+   */
+  float GetEffectiveOpacity();
+
+  /**
+   * Returns the blendmode of this layer.
+   */
+  gfx::CompositionOp GetEffectiveMixBlendMode();
+
+  /**
+   * This returns the effective transform computed by
+   * ComputeEffectiveTransforms. Typically this is a transform that transforms
+   * this layer all the way to some intermediate surface or destination
+   * surface. For non-BasicLayers this will be a transform to the nearest
+   * ancestor with UseIntermediateSurface() (or to the root, if there is no
+   * such ancestor), but for BasicLayers it's different.
+   */
+  const gfx::Matrix4x4& GetEffectiveTransform() const { return mEffectiveTransform; }
+
+  /**
+   * This returns the effective transform for Layer's buffer computed by
+   * ComputeEffectiveTransforms. Typically this is a transform that transforms
+   * this layer's buffer all the way to some intermediate surface or destination
+   * surface. For non-BasicLayers this will be a transform to the nearest
+   * ancestor with UseIntermediateSurface() (or to the root, if there is no
+   * such ancestor), but for BasicLayers it's different.
+   *
+   * By default, its value is same to GetEffectiveTransform().
+   * When ImageLayer is rendered with ScaleMode::STRETCH,
+   * it becomes different from GetEffectiveTransform().
+   */
+  virtual const gfx::Matrix4x4& GetEffectiveTransformForBuffer() const
+  {
+    return mEffectiveTransform;
+  }
+
+  /**
+   * @param aTransformToSurface the composition of the transforms
+   * from the parent layer (if any) to the destination pixel grid.
+   *
+   * Computes mEffectiveTransform for this layer and all its descendants.
+   * mEffectiveTransform transforms this layer up to the destination
+   * pixel grid (whatever aTransformToSurface is relative to).
+   *
+   * We promise that when this is called on a layer, all ancestor layers
+   * have already had ComputeEffectiveTransforms called.
+   */
+  virtual void ComputeEffectiveTransforms(const gfx::Matrix4x4& aTransformToSurface) = 0;
+
+  /**
+   * Computes the effective transform for mask layers, if this layer has any.
+   */
+  void ComputeEffectiveTransformForMaskLayers(const gfx::Matrix4x4& aTransformToSurface);
+  static void ComputeEffectiveTransformForMaskLayer(Layer* aMaskLayer,
+                                                    const gfx::Matrix4x4& aTransformToSurface);
+
+  /**
+   * Calculate the scissor rect required when rendering this layer.
+   * Returns a rectangle relative to the intermediate surface belonging to the
+   * nearest ancestor that has an intermediate surface, or relative to the root
+   * viewport if no ancestor has an intermediate surface, corresponding to the
+   * clip rect for this layer intersected with aCurrentScissorRect.
+   */
+  RenderTargetIntRect CalculateScissorRect(const RenderTargetIntRect& aCurrentScissorRect);
+
+  virtual const char* Name() const =0;
+  virtual LayerType GetType() const =0;
+
+  /**
+   * Only the implementation should call this. This is per-implementation
+   * private data. Normally, all layers with a given layer manager
+   * use the same type of ImplData.
+   */
+  void* ImplData() { return mImplData; }
+
+  /**
+   * Only the implementation should use these methods.
+   */
+  void SetParent(ContainerLayer* aParent) { mParent = aParent; }
+  void SetNextSibling(Layer* aSibling) { mNextSibling = aSibling; }
+  void SetPrevSibling(Layer* aSibling) { mPrevSibling = aSibling; }
+
+  /**
+   * Dump information about this layer manager and its managed tree to
+   * aStream.
+   */
+  void Dump(std::stringstream& aStream, const char* aPrefix="",
+            bool aDumpHtml=false, bool aSorted=false);
+  /**
+   * Dump information about just this layer manager itself to aStream.
+   */
+  void DumpSelf(std::stringstream& aStream, const char* aPrefix="");
+
+  /**
+   * Dump information about this layer and its child & sibling layers to
+   * layerscope packet.
+   */
+  void Dump(layerscope::LayersPacket* aPacket, const void* aParent);
+
+  /**
+   * Log information about this layer manager and its managed tree to
+   * the NSPR log (if enabled for "Layers").
+   */
+  void Log(const char* aPrefix="");
+  /**
+   * Log information about just this layer manager itself to the NSPR
+   * log (if enabled for "Layers").
+   */
+  void LogSelf(const char* aPrefix="");
+
+  // Print interesting information about this into aStream. Internally
+  // used to implement Dump*() and Log*(). If subclasses have
+  // additional interesting properties, they should override this with
+  // an implementation that first calls the base implementation then
+  // appends additional info to aTo.
+  virtual void PrintInfo(std::stringstream& aStream, const char* aPrefix);
+
+  // Just like PrintInfo, but this function dump information into layerscope packet,
+  // instead of a StringStream. It is also internally used to implement Dump();
+  virtual void DumpPacket(layerscope::LayersPacket* aPacket, const void* aParent);
+
+  /**
+   * Store display list log.
+   */
+  void SetDisplayListLog(const char *log);
+
+  /**
+   * Return display list log.
+   */
+  void GetDisplayListLog(nsCString& log);
+
+  static bool IsLogEnabled() { return LayerManager::IsLogEnabled(); }
+
+  /**
+   * Returns the current area of the layer (in layer-space coordinates)
+   * marked as needed to be recomposited.
+   */
+  const virtual gfx::TiledIntRegion& GetInvalidRegion() { return mInvalidRegion; }
+  void AddInvalidRegion(const nsIntRegion& aRegion) {
+    mInvalidRegion.Add(aRegion);
+  }
+
+  /**
+   * Mark the entirety of the layer's visible region as being invalid.
+   */
+  void SetInvalidRectToVisibleRegion()
+  {
+    mInvalidRegion.SetEmpty();
+    mInvalidRegion.Add(GetVisibleRegion().ToUnknownRegion());
+  }
+
+  /**
+   * Adds to the current invalid rect.
+   */
+  void AddInvalidRect(const gfx::IntRect& aRect) { mInvalidRegion.Add(aRect); }
+
+  /**
+   * Clear the invalid rect, marking the layer as being identical to what is currently
+   * composited.
+   */
+  void ClearInvalidRect() { mInvalidRegion.SetEmpty(); }
+
+  // These functions allow attaching an AsyncPanZoomController to this layer,
+  // and can be used anytime.
+  // A layer has an APZC at index aIndex only-if GetFrameMetrics(aIndex).IsScrollable();
+  // attempting to get an APZC for a non-scrollable metrics will return null.
+  // The aIndex for these functions must be less than GetScrollMetadataCount().
+  void SetAsyncPanZoomController(uint32_t aIndex, AsyncPanZoomController *controller);
+  AsyncPanZoomController* GetAsyncPanZoomController(uint32_t aIndex) const;
+  // The ScrollMetadataChanged function is used internally to ensure the APZC array length
+  // matches the frame metrics array length.
+private:
+  void ScrollMetadataChanged();
+public:
+
+  void ApplyPendingUpdatesForThisTransaction();
+
+#ifdef DEBUG
+  void SetDebugColorIndex(uint32_t aIndex) { mDebugColorIndex = aIndex; }
+  uint32_t GetDebugColorIndex() { return mDebugColorIndex; }
+#endif
+
+  virtual LayerRenderState GetRenderState() { return LayerRenderState(); }
+
+  void Mutated()
+  {
+    mManager->Mutated(this);
+  }
+
+  virtual int32_t GetMaxLayerSize() { return Manager()->GetMaxTextureSize(); }
+
+  /**
+   * Returns true if this layer's effective transform is not just
+   * a translation by integers, or if this layer or some ancestor layer
+   * is marked as having a transform that may change without a full layer
+   * transaction.
+   */
+  bool MayResample();
+
+  RenderTargetRect TransformRectToRenderTarget(const LayerIntRect& aRect);
+
+  /**
+   * Add debugging information to the layer dump.
+   */
+  void AddExtraDumpInfo(const nsACString& aStr)
+  {
+#ifdef MOZ_DUMP_PAINTING
+    mExtraDumpInfo.AppendElement(aStr);
+#endif
+  }
+
+  /**
+   * Clear debugging information. Useful for recycling.
+   */
+  void ClearExtraDumpInfo()
+  {
+#ifdef MOZ_DUMP_PAINTING
+     mExtraDumpInfo.Clear();
+#endif
+  }
+
+protected:
+  Layer(LayerManager* aManager, void* aImplData);
+
+  // Protected destructor, to discourage deletion outside of Release():
+  virtual ~Layer();
+
+  /**
+   * We can snap layer transforms for two reasons:
+   * 1) To avoid unnecessary resampling when a transform is a translation
+   * by a non-integer number of pixels.
+   * Snapping the translation to an integer number of pixels avoids
+   * blurring the layer and can be faster to composite.
+   * 2) When a layer is used to render a rectangular object, we need to
+   * emulate the rendering of rectangular inactive content and snap the
+   * edges of the rectangle to pixel boundaries. This is both to ensure
+   * layer rendering is consistent with inactive content rendering, and to
+   * avoid seams.
+   * This function implements type 1 snapping. If aTransform is a 2D
+   * translation, and this layer's layer manager has enabled snapping
+   * (which is the default), return aTransform with the translation snapped
+   * to nearest pixels. Otherwise just return aTransform. Call this when the
+   * layer does not correspond to a single rectangular content object.
+   * This function does not try to snap if aTransform has a scale, because in
+   * that case resampling is inevitable and there's no point in trying to
+   * avoid it. In fact snapping can cause problems because pixel edges in the
+   * layer's content can be rendered unpredictably (jiggling) as the scale
+   * interacts with the snapping of the translation, especially with animated
+   * transforms.
+   * @param aResidualTransform a transform to apply before the result transform
+   * in order to get the results to completely match aTransform.
+   */
+  gfx::Matrix4x4 SnapTransformTranslation(const gfx::Matrix4x4& aTransform,
+                                          gfx::Matrix* aResidualTransform);
+  gfx::Matrix4x4 SnapTransformTranslation3D(const gfx::Matrix4x4& aTransform,
+                                            gfx::Matrix* aResidualTransform);
+  /**
+   * See comment for SnapTransformTranslation.
+   * This function implements type 2 snapping. If aTransform is a translation
+   * and/or scale, transform aSnapRect by aTransform, snap to pixel boundaries,
+   * and return the transform that maps aSnapRect to that rect. Otherwise
+   * just return aTransform.
+   * @param aSnapRect a rectangle whose edges should be snapped to pixel
+   * boundaries in the destination surface.
+   * @param aResidualTransform a transform to apply before the result transform
+   * in order to get the results to completely match aTransform.
+   */
+  gfx::Matrix4x4 SnapTransform(const gfx::Matrix4x4& aTransform,
+                               const gfxRect& aSnapRect,
+                               gfx::Matrix* aResidualTransform);
+
+  LayerManager* mManager;
+  ContainerLayer* mParent;
+  Layer* mNextSibling;
+  Layer* mPrevSibling;
+  void* mImplData;
+  RefPtr<Layer> mMaskLayer;
+  nsTArray<RefPtr<Layer>> mAncestorMaskLayers;
+  // Look for out-of-bound in the middle of the structure
+  mozilla::CorruptionCanary mCanary;
+  gfx::UserData mUserData;
+  gfx::IntRect mLayerBounds;
+  LayerIntRegion mVisibleRegion;
+  nsTArray<ScrollMetadata> mScrollMetadata;
+  EventRegions mEventRegions;
+  gfx::Matrix4x4 mTransform;
+  // A mutation of |mTransform| that we've queued to be applied at the
+  // end of the next transaction (if nothing else overrides it in the
+  // meantime).
+  nsAutoPtr<gfx::Matrix4x4> mPendingTransform;
+  float mPostXScale;
+  float mPostYScale;
+  gfx::Matrix4x4 mEffectiveTransform;
+  AnimationArray mAnimations;
+  // See mPendingTransform above.
+  nsAutoPtr<AnimationArray> mPendingAnimations;
+  InfallibleTArray<AnimData> mAnimationData;
+  float mOpacity;
+  gfx::CompositionOp mMixBlendMode;
+  bool mForceIsolatedGroup;
+  Maybe<ParentLayerIntRect> mClipRect;
+  Maybe<LayerClip> mScrolledClip;
+  gfx::IntRect mTileSourceRect;
+  gfx::TiledIntRegion mInvalidRegion;
+  nsTArray<RefPtr<AsyncPanZoomController> > mApzcs;
+  uint32_t mContentFlags;
+  bool mUseTileSourceRect;
+  bool mIsFixedPosition;
+  bool mTransformIsPerspective;
+  struct FixedPositionData {
+    FrameMetrics::ViewID mScrollId;
+    LayerPoint mAnchor;
+    int32_t mSides;
+  };
+  UniquePtr<FixedPositionData> mFixedPositionData;
+  struct StickyPositionData {
+    FrameMetrics::ViewID mScrollId;
+    LayerRect mOuter;
+    LayerRect mInner;
+  };
+  nsAutoPtr<StickyPositionData> mStickyPositionData;
+  FrameMetrics::ViewID mScrollbarTargetId;
+  ScrollDirection mScrollbarDirection;
+  // The scrollbar thumb ratio is the ratio of the thumb position (in the CSS
+  // pixels of the scrollframe's parent's space) to the scroll position (in the
+  // CSS pixels of the scrollframe's space).
+  float mScrollbarThumbRatio;
+  bool mIsScrollbarContainer;
+#ifdef DEBUG
+  uint32_t mDebugColorIndex;
+#endif
+  // If this layer is used for OMTA, then this counter is used to ensure we
+  // stay in sync with the animation manager
+  uint64_t mAnimationGeneration;
+#ifdef MOZ_DUMP_PAINTING
+  nsTArray<nsCString> mExtraDumpInfo;
+#endif
+  // Store display list log.
+  nsCString mDisplayListLog;
+};
+
+/**
+ * A Layer which we can paint into. It is a conceptually
+ * infinite surface, but each PaintedLayer has an associated "valid region"
+ * of contents that it is currently storing, which is finite. PaintedLayer
+ * implementations can store content between paints.
+ *
+ * PaintedLayers are rendered into during the drawing phase of a transaction.
+ *
+ * Currently the contents of a PaintedLayer are in the device output color
+ * space.
+ */
+class PaintedLayer : public Layer {
+public:
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Tell this layer that the content in some region has changed and
+   * will need to be repainted. This area is removed from the valid
+   * region.
+   */
+  virtual void InvalidateRegion(const nsIntRegion& aRegion) = 0;
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Set whether ComputeEffectiveTransforms should compute the
+   * "residual translation" --- the translation that should be applied *before*
+   * mEffectiveTransform to get the ideal transform for this PaintedLayer.
+   * When this is true, ComputeEffectiveTransforms will compute the residual
+   * and ensure that the layer is invalidated whenever the residual changes.
+   * When it's false, a change in the residual will not trigger invalidation
+   * and GetResidualTranslation will return 0,0.
+   * So when the residual is to be ignored, set this to false for better
+   * performance.
+   */
+  void SetAllowResidualTranslation(bool aAllow) { mAllowResidualTranslation = aAllow; }
+
+  /**
+   * Can be used anytime
+   */
+  const nsIntRegion& GetValidRegion() const { return mValidRegion; }
+
+  virtual PaintedLayer* AsPaintedLayer() override { return this; }
+
+  MOZ_LAYER_DECL_NAME("PaintedLayer", TYPE_PAINTED)
+
+  virtual void ComputeEffectiveTransforms(const gfx::Matrix4x4& aTransformToSurface) override
+  {
+    gfx::Matrix4x4 idealTransform = GetLocalTransform() * aTransformToSurface;
+    gfx::Matrix residual;
+    mEffectiveTransform = SnapTransformTranslation(idealTransform,
+        mAllowResidualTranslation ? &residual : nullptr);
+    // The residual can only be a translation because SnapTransformTranslation
+    // only changes the transform if it's a translation
+    NS_ASSERTION(residual.IsTranslation(),
+                 "Residual transform can only be a translation");
+    if (!gfx::ThebesPoint(residual.GetTranslation()).WithinEpsilonOf(mResidualTranslation, 1e-3f)) {
+      mResidualTranslation = gfx::ThebesPoint(residual.GetTranslation());
+      DebugOnly<mozilla::gfx::Point> transformedOrig =
+        idealTransform.TransformPoint(mozilla::gfx::Point());
+#ifdef DEBUG
+      DebugOnly<mozilla::gfx::Point> transformed = idealTransform.TransformPoint(
+        mozilla::gfx::Point(mResidualTranslation.x, mResidualTranslation.y)
+      ) - *&transformedOrig;
+#endif
+      NS_ASSERTION(-0.5 <= (&transformed)->x && (&transformed)->x < 0.5 &&
+                   -0.5 <= (&transformed)->y && (&transformed)->y < 0.5,
+                   "Residual translation out of range");
+      mValidRegion.SetEmpty();
+    }
+    ComputeEffectiveTransformForMaskLayers(aTransformToSurface);
+  }
+
+  LayerManager::PaintedLayerCreationHint GetCreationHint() const { return mCreationHint; }
+
+  bool UsedForReadback() { return mUsedForReadback; }
+  void SetUsedForReadback(bool aUsed) { mUsedForReadback = aUsed; }
+
+  /**
+   * Returns true if aLayer is optimized for the given PaintedLayerCreationHint.
+   */
+  virtual bool IsOptimizedFor(LayerManager::PaintedLayerCreationHint aCreationHint)
+  { return true; }
+
+  /**
+   * Returns the residual translation. Apply this translation when drawing
+   * into the PaintedLayer so that when mEffectiveTransform is applied afterwards
+   * by layer compositing, the results exactly match the "ideal transform"
+   * (the product of the transform of this layer and its ancestors).
+   * Returns 0,0 unless SetAllowResidualTranslation(true) has been called.
+   * The residual translation components are always in the range [-0.5, 0.5).
+   */
+  gfxPoint GetResidualTranslation() const { return mResidualTranslation; }
+
+protected:
+  PaintedLayer(LayerManager* aManager, void* aImplData,
+              LayerManager::PaintedLayerCreationHint aCreationHint = LayerManager::NONE)
+    : Layer(aManager, aImplData)
+    , mValidRegion()
+    , mCreationHint(aCreationHint)
+    , mUsedForReadback(false)
+    , mAllowResidualTranslation(false)
+  {
+    mContentFlags = 0; // Clear NO_TEXT, NO_TEXT_OVER_TRANSPARENT
+  }
+
+  virtual void PrintInfo(std::stringstream& aStream, const char* aPrefix) override;
+
+  virtual void DumpPacket(layerscope::LayersPacket* aPacket, const void* aParent) override;
+
+  /**
+   * ComputeEffectiveTransforms snaps the ideal transform to get mEffectiveTransform.
+   * mResidualTranslation is the translation that should be applied *before*
+   * mEffectiveTransform to get the ideal transform.
+   */
+  gfxPoint mResidualTranslation;
+  nsIntRegion mValidRegion;
+  /**
+   * The creation hint that was used when constructing this layer.
+   */
+  const LayerManager::PaintedLayerCreationHint mCreationHint;
+  /**
+   * Set when this PaintedLayer is participating in readback, i.e. some
+   * ReadbackLayer (may) be getting its background from this layer.
+   */
+  bool mUsedForReadback;
+  /**
+   * True when
+   */
+  bool mAllowResidualTranslation;
+};
+
+/**
+ * A Layer which other layers render into. It holds references to its
+ * children.
+ */
+class ContainerLayer : public Layer {
+public:
+
+  ~ContainerLayer();
+
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Insert aChild into the child list of this container. aChild must
+   * not be currently in any child list or the root for the layer manager.
+   * If aAfter is non-null, it must be a child of this container and
+   * we insert after that layer. If it's null we insert at the start.
+   */
+  virtual bool InsertAfter(Layer* aChild, Layer* aAfter);
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Remove aChild from the child list of this container. aChild must
+   * be a child of this container.
+   */
+  virtual bool RemoveChild(Layer* aChild);
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Reposition aChild from the child list of this container. aChild must
+   * be a child of this container.
+   * If aAfter is non-null, it must be a child of this container and we
+   * reposition after that layer. If it's null, we reposition at the start.
+   */
+  virtual bool RepositionChild(Layer* aChild, Layer* aAfter);
+
+  void SetPreScale(float aXScale, float aYScale)
+  {
+    if (mPreXScale == aXScale && mPreYScale == aYScale) {
+      return;
+    }
+
+    MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) PreScale", this));
+    mPreXScale = aXScale;
+    mPreYScale = aYScale;
+    Mutated();
+  }
+
+  void SetInheritedScale(float aXScale, float aYScale)
+  {
+    if (mInheritedXScale == aXScale && mInheritedYScale == aYScale) {
+      return;
+    }
+
+    MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) InheritedScale", this));
+    mInheritedXScale = aXScale;
+    mInheritedYScale = aYScale;
+    Mutated();
+  }
+
+  void SetScaleToResolution(bool aScaleToResolution, float aResolution)
+  {
+    if (mScaleToResolution == aScaleToResolution && mPresShellResolution == aResolution) {
+      return;
+    }
+
+    MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) ScaleToResolution", this));
+    mScaleToResolution = aScaleToResolution;
+    mPresShellResolution = aResolution;
+    Mutated();
+  }
+
+  virtual void FillSpecificAttributes(SpecificLayerAttributes& aAttrs) override;
+
+  void SortChildrenBy3DZOrder(nsTArray<Layer*>& aArray);
+
+  // These getters can be used anytime.
+
+  virtual ContainerLayer* AsContainerLayer() override { return this; }
+  virtual const ContainerLayer* AsContainerLayer() const override { return this; }
+
+  virtual Layer* GetFirstChild() const override { return mFirstChild; }
+  virtual Layer* GetLastChild() const override { return mLastChild; }
+  float GetPreXScale() const { return mPreXScale; }
+  float GetPreYScale() const { return mPreYScale; }
+  float GetInheritedXScale() const { return mInheritedXScale; }
+  float GetInheritedYScale() const { return mInheritedYScale; }
+  float GetPresShellResolution() const { return mPresShellResolution; }
+  bool ScaleToResolution() const { return mScaleToResolution; }
+
+  MOZ_LAYER_DECL_NAME("ContainerLayer", TYPE_CONTAINER)
+
+  /**
+   * ContainerLayer backends need to override ComputeEffectiveTransforms
+   * since the decision about whether to use a temporary surface for the
+   * container is backend-specific. ComputeEffectiveTransforms must also set
+   * mUseIntermediateSurface.
+   */
+  virtual void ComputeEffectiveTransforms(const gfx::Matrix4x4& aTransformToSurface) override = 0;
+
+  /**
+   * Call this only after ComputeEffectiveTransforms has been invoked
+   * on this layer.
+   * Returns true if this will use an intermediate surface. This is largely
+   * backend-dependent, but it affects the operation of GetEffectiveOpacity().
+   */
+  bool UseIntermediateSurface() { return mUseIntermediateSurface; }
+
+  /**
+   * Returns the rectangle covered by the intermediate surface,
+   * in this layer's coordinate system.
+   *
+   * NOTE: Since this layer has an intermediate surface it follows
+   *       that LayerPixel == RenderTargetPixel
+   */
+  RenderTargetIntRect GetIntermediateSurfaceRect()
+  {
+    NS_ASSERTION(mUseIntermediateSurface, "Must have intermediate surface");
+    return RenderTargetIntRect::FromUnknownRect(GetLocalVisibleRegion().ToUnknownRegion().GetBounds());
+  }
+
+  /**
+   * Returns true if this container has more than one non-empty child
+   */
+  bool HasMultipleChildren();
+
+  /**
+   * Returns true if this container supports children with component alpha.
+   * Should only be called while painting a child of this layer.
+   */
+  bool SupportsComponentAlphaChildren() { return mSupportsComponentAlphaChildren; }
+
+  /**
+   * Returns true if aLayer or any layer in its parent chain has the opaque
+   * content flag set.
+   */
+  static bool HasOpaqueAncestorLayer(Layer* aLayer);
+
+  void SetChildrenChanged(bool aVal) {
+    mChildrenChanged = aVal;
+  }
+
+  void SetEventRegionsOverride(EventRegionsOverride aVal) {
+    if (mEventRegionsOverride == aVal) {
+      return;
+    }
+
+    MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) EventRegionsOverride", this));
+    mEventRegionsOverride = aVal;
+    Mutated();
+  }
+
+  EventRegionsOverride GetEventRegionsOverride() const {
+    return mEventRegionsOverride;
+  }
+
+protected:
+  friend class ReadbackProcessor;
+
+  void DidInsertChild(Layer* aLayer);
+  void DidRemoveChild(Layer* aLayer);
+
+  void Collect3DContextLeaves(nsTArray<Layer*>& aToSort);
+
+  ContainerLayer(LayerManager* aManager, void* aImplData);
+
+  /**
+   * A default implementation of ComputeEffectiveTransforms for use by OpenGL
+   * and D3D.
+   */
+  void DefaultComputeEffectiveTransforms(const gfx::Matrix4x4& aTransformToSurface);
+
+  /**
+   * A default implementation to compute and set the value for SupportsComponentAlphaChildren().
+   *
+   * If aNeedsSurfaceCopy is provided, then it is set to true if the caller needs to copy the background
+   * up into the intermediate surface created, false otherwise.
+   */
+  void DefaultComputeSupportsComponentAlphaChildren(bool* aNeedsSurfaceCopy = nullptr);
+
+  /**
+   * Loops over the children calling ComputeEffectiveTransforms on them.
+   */
+  void ComputeEffectiveTransformsForChildren(const gfx::Matrix4x4& aTransformToSurface);
+
+  virtual void PrintInfo(std::stringstream& aStream, const char* aPrefix) override;
+
+  virtual void DumpPacket(layerscope::LayersPacket* aPacket, const void* aParent) override;
+
+  /**
+   * True for if the container start a new 3D context extended by one
+   * or more children.
+   */
+  bool Creates3DContextWithExtendingChildren();
+
+  Layer* mFirstChild;
+  Layer* mLastChild;
+  float mPreXScale;
+  float mPreYScale;
+  // The resolution scale inherited from the parent layer. This will already
+  // be part of mTransform.
+  float mInheritedXScale;
+  float mInheritedYScale;
+  // For layers corresponding to an nsDisplayResolution, the resolution of the
+  // associated pres shell; for other layers, 1.0.
+  float mPresShellResolution;
+  // Whether the compositor should scale to mPresShellResolution.
+  bool mScaleToResolution;
+  bool mUseIntermediateSurface;
+  bool mSupportsComponentAlphaChildren;
+  bool mMayHaveReadbackChild;
+  // This is updated by ComputeDifferences. This will be true if we need to invalidate
+  // the intermediate surface.
+  bool mChildrenChanged;
+  EventRegionsOverride mEventRegionsOverride;
+};
+
+/**
+ * A Layer which just renders a solid color in its visible region. It actually
+ * can fill any area that contains the visible region, so if you need to
+ * restrict the area filled, set a clip region on this layer.
+ */
+class ColorLayer : public Layer {
+public:
+  virtual ColorLayer* AsColorLayer() override { return this; }
+
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Set the color of the layer.
+   */
+  virtual void SetColor(const gfx::Color& aColor)
+  {
+    if (mColor != aColor) {
+      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) Color", this));
+      mColor = aColor;
+      Mutated();
+    }
+  }
+
+  void SetBounds(const gfx::IntRect& aBounds)
+  {
+    if (!mBounds.IsEqualEdges(aBounds)) {
+      mBounds = aBounds;
+      Mutated();
+    }
+  }
+
+  const gfx::IntRect& GetBounds()
+  {
+    return mBounds;
+  }
+
+  // This getter can be used anytime.
+  virtual const gfx::Color& GetColor() { return mColor; }
+
+  MOZ_LAYER_DECL_NAME("ColorLayer", TYPE_COLOR)
+
+  virtual void ComputeEffectiveTransforms(const gfx::Matrix4x4& aTransformToSurface) override
+  {
+    gfx::Matrix4x4 idealTransform = GetLocalTransform() * aTransformToSurface;
+    mEffectiveTransform = SnapTransformTranslation(idealTransform, nullptr);
+    ComputeEffectiveTransformForMaskLayers(aTransformToSurface);
+  }
+
+protected:
+  ColorLayer(LayerManager* aManager, void* aImplData)
+    : Layer(aManager, aImplData)
+    , mColor()
+  {}
+
+  virtual void PrintInfo(std::stringstream& aStream, const char* aPrefix) override;
+
+  virtual void DumpPacket(layerscope::LayersPacket* aPacket, const void* aParent) override;
+
+  gfx::IntRect mBounds;
+  gfx::Color mColor;
+};
+
+/**
+ * A Layer for HTML Canvas elements.  It's backed by either a
+ * gfxASurface or a GLContext (for WebGL layers), and has some control
+ * for intelligent updating from the source if necessary (for example,
+ * if hardware compositing is not available, for reading from the GL
+ * buffer into an image surface that we can layer composite.)
+ *
+ * After Initialize is called, the underlying canvas Surface/GLContext
+ * must not be modified during a layer transaction.
+ */
+class CanvasLayer : public Layer {
+public:
+  struct Data {
+    Data()
+      : mBufferProvider(nullptr)
+      , mGLContext(nullptr)
+      , mRenderer(nullptr)
+      , mFrontbufferGLTex(0)
+      , mSize(0,0)
+      , mHasAlpha(false)
+      , mIsGLAlphaPremult(true)
+      , mIsMirror(false)
+    { }
+
+    // One of these three must be specified for Canvas2D, but never more than one
+    PersistentBufferProvider* mBufferProvider; // A BufferProvider for the Canvas contents
+    mozilla::gl::GLContext* mGLContext; // or this, for GL.
+    AsyncCanvasRenderer* mRenderer; // or this, for OffscreenCanvas
+
+    // Frontbuffer override
+    uint32_t mFrontbufferGLTex;
+
+    // The size of the canvas content
+    gfx::IntSize mSize;
+
+    // Whether the canvas drawingbuffer has an alpha channel.
+    bool mHasAlpha;
+
+    // Whether mGLContext contains data that is alpha-premultiplied.
+    bool mIsGLAlphaPremult;
+
+    // Whether the canvas front buffer is already being rendered somewhere else.
+    // When true, do not swap buffers or Morph() to another factory on mGLContext
+    bool mIsMirror;
+  };
+
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Initialize this CanvasLayer with the given data.  The data must
+   * have either mSurface or mGLContext initialized (but not both), as
+   * well as mSize.
+   *
+   * This must only be called once.
+   */
+  virtual void Initialize(const Data& aData) = 0;
+
+  /**
+   * Check the data is owned by this layer is still valid for rendering
+   */
+  virtual bool IsDataValid(const Data& aData) { return true; }
+
+  /**
+   * Notify this CanvasLayer that the canvas surface contents have
+   * changed (or will change) before the next transaction.
+   */
+  void Updated() { mDirty = true; SetInvalidRectToVisibleRegion(); }
+
+  /**
+   * Notify this CanvasLayer that the canvas surface contents have
+   * been painted since the last change.
+   */
+  void Painted() { mDirty = false; }
+
+  /**
+   * Returns true if the canvas surface contents have changed since the
+   * last paint.
+   */
+  bool IsDirty()
+  {
+    // We can only tell if we are dirty if we're part of the
+    // widget's retained layer tree.
+    if (!mManager || !mManager->IsWidgetLayerManager()) {
+      return true;
+    }
+    return mDirty;
+  }
+
+  /**
+   * Register a callback to be called at the start of each transaction.
+   */
+  typedef void PreTransactionCallback(void* closureData);
+  void SetPreTransactionCallback(PreTransactionCallback* callback, void* closureData)
+  {
+    mPreTransCallback = callback;
+    mPreTransCallbackData = closureData;
+  }
+
+  const nsIntRect& GetBounds() const { return mBounds; }
+
+protected:
+  void FirePreTransactionCallback()
+  {
+    if (mPreTransCallback) {
+      mPreTransCallback(mPreTransCallbackData);
+    }
+  }
+
+public:
+  /**
+   * Register a callback to be called at the end of each transaction.
+   */
+  typedef void (* DidTransactionCallback)(void* aClosureData);
+  void SetDidTransactionCallback(DidTransactionCallback aCallback, void* aClosureData)
+  {
+    mPostTransCallback = aCallback;
+    mPostTransCallbackData = aClosureData;
+  }
+
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Set the filter used to resample this image (if necessary).
+   */
+  void SetSamplingFilter(gfx::SamplingFilter aSamplingFilter)
+  {
+    if (mSamplingFilter != aSamplingFilter) {
+      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) Filter", this));
+      mSamplingFilter = aSamplingFilter;
+      Mutated();
+    }
+  }
+  gfx::SamplingFilter GetSamplingFilter() const { return mSamplingFilter; }
+
+  MOZ_LAYER_DECL_NAME("CanvasLayer", TYPE_CANVAS)
+
+  virtual void ComputeEffectiveTransforms(const gfx::Matrix4x4& aTransformToSurface) override
+  {
+    // Snap our local transform first, and snap the inherited transform as well.
+    // This makes our snapping equivalent to what would happen if our content
+    // was drawn into a PaintedLayer (gfxContext would snap using the local
+    // transform, then we'd snap again when compositing the PaintedLayer).
+    mEffectiveTransform =
+        SnapTransform(GetLocalTransform(), gfxRect(0, 0, mBounds.width, mBounds.height),
+                      nullptr)*
+        SnapTransformTranslation(aTransformToSurface, nullptr);
+    ComputeEffectiveTransformForMaskLayers(aTransformToSurface);
+  }
+
+  bool GetIsAsyncRenderer() const
+  {
+    return !!mAsyncRenderer;
+  }
+
+protected:
+  CanvasLayer(LayerManager* aManager, void* aImplData);
+  virtual ~CanvasLayer();
+
+  virtual void PrintInfo(std::stringstream& aStream, const char* aPrefix) override;
+
+  virtual void DumpPacket(layerscope::LayersPacket* aPacket, const void* aParent) override;
+
+  void FireDidTransactionCallback()
+  {
+    if (mPostTransCallback) {
+      mPostTransCallback(mPostTransCallbackData);
+    }
+  }
+
+  /**
+   * 0, 0, canvaswidth, canvasheight
+   */
+  gfx::IntRect mBounds;
+  PreTransactionCallback* mPreTransCallback;
+  void* mPreTransCallbackData;
+  DidTransactionCallback mPostTransCallback;
+  void* mPostTransCallbackData;
+  gfx::SamplingFilter mSamplingFilter;
+  RefPtr<AsyncCanvasRenderer> mAsyncRenderer;
+
+private:
+  /**
+   * Set to true in Updated(), cleared during a transaction.
+   */
+  bool mDirty;
+};
+
+/**
+ * ContainerLayer that refers to a "foreign" layer tree, through an
+ * ID.  Usage of RefLayer looks like
+ *
+ * Construction phase:
+ *   allocate ID for layer subtree
+ *   create RefLayer, SetReferentId(ID)
+ *
+ * Composition:
+ *   look up subtree for GetReferentId()
+ *   ConnectReferentLayer(subtree)
+ *   compose
+ *   ClearReferentLayer()
+ *
+ * Clients will usually want to Connect/Clear() on each transaction to
+ * avoid difficulties managing memory across multiple layer subtrees.
+ */
+class RefLayer : public ContainerLayer {
+  friend class LayerManager;
+
+private:
+  virtual bool InsertAfter(Layer* aChild, Layer* aAfter) override
+  { MOZ_CRASH("GFX: RefLayer"); return false; }
+
+  virtual bool RemoveChild(Layer* aChild) override
+  { MOZ_CRASH("GFX: RefLayer"); return false; }
+
+  virtual bool RepositionChild(Layer* aChild, Layer* aAfter) override
+  { MOZ_CRASH("GFX: RefLayer"); return false; }
+
+public:
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Set the ID of the layer's referent.
+   */
+  void SetReferentId(uint64_t aId)
+  {
+    MOZ_ASSERT(aId != 0);
+    if (mId != aId) {
+      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) ReferentId", this));
+      mId = aId;
+      Mutated();
+    }
+  }
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Connect this ref layer to its referent, temporarily.
+   * ClearReferentLayer() must be called after composition.
+   */
+  void ConnectReferentLayer(Layer* aLayer)
+  {
+    MOZ_ASSERT(!mFirstChild && !mLastChild);
+    MOZ_ASSERT(!aLayer->GetParent());
+    if (aLayer->Manager() != Manager()) {
+      // This can happen when e.g. rendering while dragging tabs
+      // between windows - aLayer's manager may be the manager for the
+      // old window's tab.  In that case, it will be changed before the
+      // next render (see SetLayerManager).  It is simply easier to
+      // ignore the rendering here than it is to pause it.
+      NS_WARNING("ConnectReferentLayer failed - Incorrect LayerManager");
+      return;
+    }
+
+    mFirstChild = mLastChild = aLayer;
+    aLayer->SetParent(this);
+  }
+
+  /**
+   * DRAWING PHASE ONLY
+   * |aLayer| is the same as the argument to ConnectReferentLayer().
+   */
+  void DetachReferentLayer(Layer* aLayer)
+  {
+    mFirstChild = mLastChild = nullptr;
+    aLayer->SetParent(nullptr);
+  }
+
+  // These getters can be used anytime.
+  virtual RefLayer* AsRefLayer() override { return this; }
+
+  virtual int64_t GetReferentId() { return mId; }
+
+  /**
+   * DRAWING PHASE ONLY
+   */
+  virtual void FillSpecificAttributes(SpecificLayerAttributes& aAttrs) override;
+
+  MOZ_LAYER_DECL_NAME("RefLayer", TYPE_REF)
+
+protected:
+  RefLayer(LayerManager* aManager, void* aImplData)
+    : ContainerLayer(aManager, aImplData) , mId(0)
+  {}
+
+  virtual void PrintInfo(std::stringstream& aStream, const char* aPrefix) override;
+
+  virtual void DumpPacket(layerscope::LayersPacket* aPacket, const void* aParent) override;
+
+  // 0 is a special value that means "no ID".
+  uint64_t mId;
+};
+
+void SetAntialiasingFlags(Layer* aLayer, gfx::DrawTarget* aTarget);
+
+#ifdef MOZ_DUMP_PAINTING
+void WriteSnapshotToDumpFile(Layer* aLayer, gfx::DataSourceSurface* aSurf);
+void WriteSnapshotToDumpFile(LayerManager* aManager, gfx::DataSourceSurface* aSurf);
+void WriteSnapshotToDumpFile(Compositor* aCompositor, gfx::DrawTarget* aTarget);
+#endif
+
+// A utility function used by different LayerManager implementations.
+gfx::IntRect ToOutsideIntRect(const gfxRect &aRect);
+
+} // namespace layers
+} // namespace mozilla
+
+#endif /* GFX_LAYERS_H */