Add m-esr52 at 52.6.0

1 files changed, 1498 insertions, 0 deletions

diff --git a/layout/generic/nsGfxScrollFrame.h b/layout/generic/nsGfxScrollFrame.h
new file mode 100644
index 000000000..f1ef44ae8
--- /dev/null
+++ b/layout/generic/nsGfxScrollFrame.h
@@ -0,0 +1,1498 @@
+/* -*- 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/. */
+
+/* rendering object to wrap rendering objects that should be scrollable */
+
+#ifndef nsGfxScrollFrame_h___
+#define nsGfxScrollFrame_h___
+
+#include "mozilla/Attributes.h"
+#include "nsContainerFrame.h"
+#include "nsIAnonymousContentCreator.h"
+#include "nsBoxFrame.h"
+#include "nsIScrollableFrame.h"
+#include "nsIScrollbarMediator.h"
+#include "nsIStatefulFrame.h"
+#include "nsThreadUtils.h"
+#include "nsIReflowCallback.h"
+#include "nsBoxLayoutState.h"
+#include "nsQueryFrame.h"
+#include "nsRefreshDriver.h"
+#include "nsExpirationTracker.h"
+#include "TextOverflow.h"
+#include "ScrollVelocityQueue.h"
+
+class nsPresContext;
+class nsIPresShell;
+class nsIContent;
+class nsIAtom;
+class nsPresState;
+class nsIScrollPositionListener;
+
+namespace mozilla {
+struct ScrollReflowInput;
+namespace layers {
+class Layer;
+} // namespace layers
+namespace layout {
+class ScrollbarActivity;
+} // namespace layout
+
+class ScrollFrameHelper : public nsIReflowCallback {
+public:
+  typedef nsIFrame::Sides Sides;
+  typedef mozilla::CSSIntPoint CSSIntPoint;
+  typedef mozilla::layout::ScrollbarActivity ScrollbarActivity;
+  typedef mozilla::layers::FrameMetrics FrameMetrics;
+  typedef mozilla::layers::ScrollSnapInfo ScrollSnapInfo;
+  typedef mozilla::layers::Layer Layer;
+
+  class AsyncScroll;
+  class AsyncSmoothMSDScroll;
+
+  ScrollFrameHelper(nsContainerFrame* aOuter, bool aIsRoot);
+  ~ScrollFrameHelper();
+
+  mozilla::ScrollbarStyles GetScrollbarStylesFromFrame() const;
+
+  // If a child frame was added or removed on the scrollframe,
+  // reload our child frame list.
+  // We need this if a scrollbar frame is recreated.
+  void ReloadChildFrames();
+
+  nsresult CreateAnonymousContent(
+    nsTArray<nsIAnonymousContentCreator::ContentInfo>& aElements);
+  void AppendAnonymousContentTo(nsTArray<nsIContent*>& aElements, uint32_t aFilter);
+  nsresult FireScrollPortEvent();
+  void PostOverflowEvent();
+  void Destroy();
+
+  void BuildDisplayList(nsDisplayListBuilder*   aBuilder,
+                        const nsRect&           aDirtyRect,
+                        const nsDisplayListSet& aLists);
+
+  void AppendScrollPartsTo(nsDisplayListBuilder*   aBuilder,
+                           const nsRect&           aDirtyRect,
+                           const nsDisplayListSet& aLists,
+                           bool                    aCreateLayer,
+                           bool                    aPositioned);
+
+  bool GetBorderRadii(const nsSize& aFrameSize, const nsSize& aBorderArea,
+                      Sides aSkipSides, nscoord aRadii[8]) const;
+
+  // nsIReflowCallback
+  virtual bool ReflowFinished() override;
+  virtual void ReflowCallbackCanceled() override;
+
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   * Called when the 'curpos' attribute on one of the scrollbars changes.
+   */
+  void CurPosAttributeChanged(nsIContent* aChild);
+
+  void PostScrollEvent();
+  void FireScrollEvent();
+  void PostScrolledAreaEvent();
+  void FireScrolledAreaEvent();
+
+  bool IsSmoothScrollingEnabled();
+
+  /**
+   * This class handles the dispatching of scroll events to content.
+   *
+   * nsRefreshDriver maintains three lists of refresh observers, one for each
+   * flush type: Flush_Style, Flush_Layout, and Flush_Display.
+   *
+   * During a tick, it runs through each list of observers, in order, and runs
+   * them. To iterate over each list, it uses an EndLimitedIterator, which is
+   * designed to iterate only over elements present when the iterator was
+   * created, not elements added afterwards. This means that, for a given flush
+   * type, a refresh observer added during the execution of another refresh
+   * observer of that flush type, will not run until the next tick.
+   *
+   * During main-thread animation-driven scrolling, ScrollEvents are *posted*
+   * by AsyncScroll::WillRefresh(). AsyncScroll registers itself as a Flush_Style
+   * refresh observer.
+   *
+   * Posting a scroll event, as of bug 1250550, registers a Flush_Layout
+   * refresh observer, which *fires* the event when run. This allows the event
+   * to be fired to content in the same refresh driver tick as it is posted.
+   * This is an important invariant to maintain to reduce scroll event latency
+   * for main-thread scrolling.
+   */
+  class ScrollEvent : public nsARefreshObserver {
+  public:
+    NS_INLINE_DECL_REFCOUNTING(ScrollEvent, override)
+    explicit ScrollEvent(ScrollFrameHelper *helper);
+    void WillRefresh(mozilla::TimeStamp aTime) override;
+  protected:
+    virtual ~ScrollEvent();
+  private:
+    ScrollFrameHelper *mHelper;
+    RefPtr<nsRefreshDriver> mDriver;
+  };
+
+  class AsyncScrollPortEvent : public Runnable {
+  public:
+    NS_DECL_NSIRUNNABLE
+    explicit AsyncScrollPortEvent(ScrollFrameHelper *helper) : mHelper(helper) {}
+    void Revoke() { mHelper = nullptr; }
+  private:
+    ScrollFrameHelper *mHelper;
+  };
+
+  class ScrolledAreaEvent : public Runnable {
+  public:
+    NS_DECL_NSIRUNNABLE
+    explicit ScrolledAreaEvent(ScrollFrameHelper *helper) : mHelper(helper) {}
+    void Revoke() { mHelper = nullptr; }
+  private:
+    ScrollFrameHelper *mHelper;
+  };
+
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void FinishReflowForScrollbar(nsIContent* aContent, nscoord aMinXY,
+                                nscoord aMaxXY, nscoord aCurPosXY,
+                                nscoord aPageIncrement,
+                                nscoord aIncrement);
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void SetScrollbarEnabled(nsIContent* aContent, nscoord aMaxPos);
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void SetCoordAttribute(nsIContent* aContent, nsIAtom* aAtom, nscoord aSize);
+
+  nscoord GetCoordAttribute(nsIFrame* aFrame, nsIAtom* aAtom, nscoord aDefaultValue,
+                            nscoord* aRangeStart, nscoord* aRangeLength);
+
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   * Update scrollbar curpos attributes to reflect current scroll position
+   */
+  void UpdateScrollbarPosition();
+
+  nsRect GetScrollPortRect() const { return mScrollPort; }
+  nsPoint GetScrollPosition() const {
+    return mScrollPort.TopLeft() - mScrolledFrame->GetPosition();
+  }
+  /**
+   * For LTR frames, the logical scroll position is the offset of the top left
+   * corner of the frame from the top left corner of the scroll port (same as
+   * GetScrollPosition).
+   * For RTL frames, it is the offset of the top right corner of the frame from
+   * the top right corner of the scroll port
+   */
+  nsPoint GetLogicalScrollPosition() const {
+    nsPoint pt;
+    pt.x = IsPhysicalLTR() ?
+      mScrollPort.x - mScrolledFrame->GetPosition().x :
+      mScrollPort.XMost() - mScrolledFrame->GetRect().XMost();
+    pt.y = mScrollPort.y - mScrolledFrame->GetPosition().y;
+    return pt;
+  }
+  nsRect GetScrollRange() const;
+  // Get the scroll range assuming the scrollport has size (aWidth, aHeight).
+  nsRect GetScrollRange(nscoord aWidth, nscoord aHeight) const;
+  nsSize GetScrollPositionClampingScrollPortSize() const;
+  void ScrollSnap(nsIScrollableFrame::ScrollMode aMode = nsIScrollableFrame::SMOOTH_MSD);
+  void ScrollSnap(const nsPoint &aDestination,
+                  nsIScrollableFrame::ScrollMode aMode = nsIScrollableFrame::SMOOTH_MSD);
+
+protected:
+  nsRect GetScrollRangeForClamping() const;
+
+public:
+  static void AsyncScrollCallback(ScrollFrameHelper* aInstance,
+                                  mozilla::TimeStamp aTime);
+  static void AsyncSmoothMSDScrollCallback(ScrollFrameHelper* aInstance,
+                                           mozilla::TimeDuration aDeltaTime);
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   * aRange is the range of allowable scroll positions around the desired
+   * aScrollPosition. Null means only aScrollPosition is allowed.
+   * This is a closed-ended range --- aRange.XMost()/aRange.YMost() are allowed.
+   */
+  void ScrollTo(nsPoint aScrollPosition, nsIScrollableFrame::ScrollMode aMode,
+                const nsRect* aRange = nullptr,
+                nsIScrollbarMediator::ScrollSnapMode aSnap
+                  = nsIScrollbarMediator::DISABLE_SNAP) {
+    ScrollToWithOrigin(aScrollPosition, aMode, nsGkAtoms::other, aRange,
+                       aSnap);
+  }
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void ScrollToCSSPixels(const CSSIntPoint& aScrollPosition,
+                         nsIScrollableFrame::ScrollMode aMode
+                           = nsIScrollableFrame::INSTANT);
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void ScrollToCSSPixelsApproximate(const mozilla::CSSPoint& aScrollPosition,
+                                    nsIAtom* aOrigin = nullptr);
+
+  CSSIntPoint GetScrollPositionCSSPixels();
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void ScrollToImpl(nsPoint aScrollPosition, const nsRect& aRange, nsIAtom* aOrigin = nullptr);
+  void ScrollVisual();
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void ScrollBy(nsIntPoint aDelta, nsIScrollableFrame::ScrollUnit aUnit,
+                nsIScrollableFrame::ScrollMode aMode, nsIntPoint* aOverflow,
+                nsIAtom* aOrigin = nullptr,
+                nsIScrollableFrame::ScrollMomentum aMomentum = nsIScrollableFrame::NOT_MOMENTUM,
+                nsIScrollbarMediator::ScrollSnapMode aSnap
+                  = nsIScrollbarMediator::DISABLE_SNAP);
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void ScrollToRestoredPosition();
+
+  bool PageIsStillLoading();
+
+  /**
+   * GetSnapPointForDestination determines which point to snap to after
+   * scrolling. aStartPos gives the position before scrolling and aDestination
+   * gives the position after scrolling, with no snapping. Behaviour is
+   * dependent on the value of aUnit.
+   * Returns true if a suitable snap point could be found and aDestination has
+   * been updated to a valid snapping position.
+   */
+  bool GetSnapPointForDestination(nsIScrollableFrame::ScrollUnit aUnit,
+                                  nsPoint aStartPos,
+                                  nsPoint &aDestination);
+
+  nsSize GetLineScrollAmount() const;
+  nsSize GetPageScrollAmount() const;
+
+  nsPresState* SaveState() const;
+  void RestoreState(nsPresState* aState);
+
+  nsIFrame* GetScrolledFrame() const { return mScrolledFrame; }
+  nsIFrame* GetScrollbarBox(bool aVertical) const {
+    return aVertical ? mVScrollbarBox : mHScrollbarBox;
+  }
+
+  void AddScrollPositionListener(nsIScrollPositionListener* aListener) {
+    mListeners.AppendElement(aListener);
+  }
+  void RemoveScrollPositionListener(nsIScrollPositionListener* aListener) {
+    mListeners.RemoveElement(aListener);
+  }
+
+  static void SetScrollbarVisibility(nsIFrame* aScrollbar, bool aVisible);
+
+  /**
+   * GetScrolledRect is designed to encapsulate deciding which
+   * directions of overflow should be reachable by scrolling and which
+   * should not.  Callers should NOT depend on it having any particular
+   * behavior (although nsXULScrollFrame currently does).
+   * 
+   * This should only be called when the scrolled frame has been
+   * reflowed with the scroll port size given in mScrollPort.
+   *
+   * Currently it allows scrolling down and to the right for
+   * nsHTMLScrollFrames with LTR directionality and for all
+   * nsXULScrollFrames, and allows scrolling down and to the left for
+   * nsHTMLScrollFrames with RTL directionality.
+   */
+  nsRect GetScrolledRect() const;
+
+  /**
+   * GetUnsnappedScrolledRectInternal is designed to encapsulate deciding which
+   * directions of overflow should be reachable by scrolling and which
+   * should not.  Callers should NOT depend on it having any particular
+   * behavior (although nsXULScrollFrame currently does).
+   * 
+   * Currently it allows scrolling down and to the right for
+   * nsHTMLScrollFrames with LTR directionality and for all
+   * nsXULScrollFrames, and allows scrolling down and to the left for
+   * nsHTMLScrollFrames with RTL directionality.
+   */
+  nsRect GetUnsnappedScrolledRectInternal(const nsRect& aScrolledOverflowArea,
+                                          const nsSize& aScrollPortSize) const;
+
+  uint32_t GetScrollbarVisibility() const {
+    return (mHasVerticalScrollbar ? nsIScrollableFrame::VERTICAL : 0) |
+           (mHasHorizontalScrollbar ? nsIScrollableFrame::HORIZONTAL : 0);
+  }
+  nsMargin GetActualScrollbarSizes() const;
+  nsMargin GetDesiredScrollbarSizes(nsBoxLayoutState* aState);
+  nscoord GetNondisappearingScrollbarWidth(nsBoxLayoutState* aState,
+                                           mozilla::WritingMode aVerticalWM);
+  bool IsPhysicalLTR() const {
+    WritingMode wm = GetFrameForDir()->GetWritingMode();
+    return wm.IsVertical() ? wm.IsVerticalLR() : wm.IsBidiLTR();
+  }
+  bool IsBidiLTR() const {
+    nsIFrame* frame = GetFrameForDir();
+    return frame->StyleVisibility()->mDirection == NS_STYLE_DIRECTION_LTR;
+  }
+private:
+  nsIFrame* GetFrameForDir() const; // helper for Is{Physical,Bidi}LTR to find
+                                    // the frame whose directionality we use
+
+public:
+  bool IsScrollbarOnRight() const;
+  bool IsScrollingActive(nsDisplayListBuilder* aBuilder) const;
+  bool IsMaybeScrollingActive() const;
+  bool IsProcessingAsyncScroll() const {
+    return mAsyncScroll != nullptr || mAsyncSmoothMSDScroll != nullptr;
+  }
+  void ResetScrollPositionForLayerPixelAlignment()
+  {
+    mScrollPosForLayerPixelAlignment = GetScrollPosition();
+  }
+
+  bool ComputeCustomOverflow(nsOverflowAreas& aOverflowAreas);
+
+  void UpdateSticky();
+
+  void UpdatePrevScrolledRect();
+
+  bool IsRectNearlyVisible(const nsRect& aRect) const;
+  nsRect ExpandRectToNearlyVisible(const nsRect& aRect) const;
+
+  // adjust the scrollbar rectangle aRect to account for any visible resizer.
+  // aHasResizer specifies if there is a content resizer, however this method
+  // will also check if a widget resizer is present as well.
+  void AdjustScrollbarRectForResizer(nsIFrame* aFrame, nsPresContext* aPresContext,
+                                     nsRect& aRect, bool aHasResizer, bool aVertical);
+  // returns true if a resizer should be visible
+  bool HasResizer() { return mResizerBox && !mCollapsedResizer; }
+  void LayoutScrollbars(nsBoxLayoutState& aState,
+                        const nsRect& aContentArea,
+                        const nsRect& aOldScrollArea);
+
+  bool IsIgnoringViewportClipping() const;
+
+  void MarkScrollbarsDirtyForReflow() const;
+
+  bool ShouldClampScrollPosition() const;
+
+  bool IsAlwaysActive() const;
+  void MarkRecentlyScrolled();
+  void MarkNotRecentlyScrolled();
+  nsExpirationState* GetExpirationState() { return &mActivityExpirationState; }
+
+  void SetTransformingByAPZ(bool aTransforming) {
+    mTransformingByAPZ = aTransforming;
+    if (!mozilla::css::TextOverflow::HasClippedOverflow(mOuter)) {
+      // If the block has some text-overflow stuff we should kick off a paint
+      // because we have special behaviour for it when APZ scrolling is active.
+      mOuter->SchedulePaint();
+    }
+  }
+  bool IsTransformingByAPZ() const {
+    return mTransformingByAPZ;
+  }
+  void SetScrollableByAPZ(bool aScrollable);
+  void SetZoomableByAPZ(bool aZoomable);
+  void SetScrollsClipOnUnscrolledOutOfFlow();
+
+  bool UsesContainerScrolling() const;
+
+  ScrollSnapInfo GetScrollSnapInfo() const;
+
+  bool DecideScrollableLayer(nsDisplayListBuilder* aBuilder,
+                             nsRect* aDirtyRect,
+                             bool aAllowCreateDisplayPort);
+  void NotifyApproximateFrameVisibilityUpdate();
+  bool GetDisplayPortAtLastApproximateFrameVisibilityUpdate(nsRect* aDisplayPort);
+
+  bool AllowDisplayPortExpiration();
+  void TriggerDisplayPortExpiration();
+  void ResetDisplayPortExpiryTimer();
+
+  void ScheduleSyntheticMouseMove();
+  static void ScrollActivityCallback(nsITimer *aTimer, void* anInstance);
+
+  void HandleScrollbarStyleSwitching();
+
+  nsIAtom* LastScrollOrigin() const { return mLastScrollOrigin; }
+  void AllowScrollOriginDowngrade() { mAllowScrollOriginDowngrade = true; }
+  nsIAtom* LastSmoothScrollOrigin() const { return mLastSmoothScrollOrigin; }
+  uint32_t CurrentScrollGeneration() const { return mScrollGeneration; }
+  nsPoint LastScrollDestination() const { return mDestination; }
+  void ResetScrollInfoIfGeneration(uint32_t aGeneration) {
+    if (aGeneration == mScrollGeneration) {
+      mLastScrollOrigin = nullptr;
+      mLastSmoothScrollOrigin = nullptr;
+    }
+  }
+  bool WantAsyncScroll() const;
+  Maybe<mozilla::layers::ScrollMetadata> ComputeScrollMetadata(
+    Layer* aLayer, nsIFrame* aContainerReferenceFrame,
+    const ContainerLayerParameters& aParameters,
+    const mozilla::DisplayItemClip* aClip) const;
+
+  // nsIScrollbarMediator
+  void ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                    nsIScrollbarMediator::ScrollSnapMode aSnap
+                      = nsIScrollbarMediator::DISABLE_SNAP);
+  void ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                     nsIScrollbarMediator::ScrollSnapMode aSnap
+                       = nsIScrollbarMediator::DISABLE_SNAP);
+  void ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                    nsIScrollbarMediator::ScrollSnapMode aSnap
+                      = nsIScrollbarMediator::DISABLE_SNAP);
+  void RepeatButtonScroll(nsScrollbarFrame* aScrollbar);
+  void ThumbMoved(nsScrollbarFrame* aScrollbar,
+                  nscoord aOldPos,
+                  nscoord aNewPos);
+  void ScrollbarReleased(nsScrollbarFrame* aScrollbar);
+  void ScrollByUnit(nsScrollbarFrame* aScrollbar,
+                    nsIScrollableFrame::ScrollMode aMode,
+                    int32_t aDirection,
+                    nsIScrollableFrame::ScrollUnit aUnit,
+                    nsIScrollbarMediator::ScrollSnapMode aSnap
+                      = nsIScrollbarMediator::DISABLE_SNAP);
+  bool ShouldSuppressScrollbarRepaints() const {
+    return mSuppressScrollbarRepaints;
+  }
+
+  // owning references to the nsIAnonymousContentCreator-built content
+  nsCOMPtr<nsIContent> mHScrollbarContent;
+  nsCOMPtr<nsIContent> mVScrollbarContent;
+  nsCOMPtr<nsIContent> mScrollCornerContent;
+  nsCOMPtr<nsIContent> mResizerContent;
+
+  RefPtr<ScrollEvent> mScrollEvent;
+  nsRevocableEventPtr<AsyncScrollPortEvent> mAsyncScrollPortEvent;
+  nsRevocableEventPtr<ScrolledAreaEvent> mScrolledAreaEvent;
+  nsIFrame* mHScrollbarBox;
+  nsIFrame* mVScrollbarBox;
+  nsIFrame* mScrolledFrame;
+  nsIFrame* mScrollCornerBox;
+  nsIFrame* mResizerBox;
+  nsContainerFrame* mOuter;
+  RefPtr<AsyncScroll> mAsyncScroll;
+  RefPtr<AsyncSmoothMSDScroll> mAsyncSmoothMSDScroll;
+  RefPtr<ScrollbarActivity> mScrollbarActivity;
+  nsTArray<nsIScrollPositionListener*> mListeners;
+  nsIAtom* mLastScrollOrigin;
+  bool mAllowScrollOriginDowngrade;
+  nsIAtom* mLastSmoothScrollOrigin;
+  Maybe<nsPoint> mApzSmoothScrollDestination;
+  uint32_t mScrollGeneration;
+  nsRect mScrollPort;
+  // Where we're currently scrolling to, if we're scrolling asynchronously.
+  // If we're not in the middle of an asynchronous scroll then this is
+  // just the current scroll position. ScrollBy will choose its
+  // destination based on this value.
+  nsPoint mDestination;
+  nsPoint mScrollPosAtLastPaint;
+
+  // A goal position to try to scroll to as content loads. As long as mLastPos
+  // matches the current logical scroll position, we try to scroll to mRestorePos
+  // after every reflow --- because after each time content is loaded/added to the
+  // scrollable element, there will be a reflow.
+  nsPoint mRestorePos;
+  // The last logical position we scrolled to while trying to restore mRestorePos, or
+  // 0,0 when this is a new frame. Set to -1,-1 once we've scrolled for any reason
+  // other than trying to restore mRestorePos.
+  nsPoint mLastPos;
+
+  nsExpirationState mActivityExpirationState;
+
+  nsCOMPtr<nsITimer> mScrollActivityTimer;
+  nsPoint mScrollPosForLayerPixelAlignment;
+
+  // The scroll position where we last updated frame visibility.
+  nsPoint mLastUpdateFramesPos;
+  bool mHadDisplayPortAtLastFrameUpdate;
+  nsRect mDisplayPortAtLastFrameUpdate;
+
+  nsRect mPrevScrolledRect;
+
+  FrameMetrics::ViewID mScrollParentID;
+
+  // Timer to remove the displayport some time after scrolling has stopped
+  nsCOMPtr<nsITimer> mDisplayPortExpiryTimer;
+
+  bool mNeverHasVerticalScrollbar:1;
+  bool mNeverHasHorizontalScrollbar:1;
+  bool mHasVerticalScrollbar:1;
+  bool mHasHorizontalScrollbar:1;
+  bool mFrameIsUpdatingScrollbar:1;
+  bool mDidHistoryRestore:1;
+  // Is this the scrollframe for the document's viewport?
+  bool mIsRoot:1;
+  // True if we should clip all descendants, false if we should only clip
+  // descendants for which we are the containing block.
+  bool mClipAllDescendants:1;
+  // If true, don't try to layout the scrollbars in Reflow().  This can be
+  // useful if multiple passes are involved, because we don't want to place the
+  // scrollbars at the wrong size.
+  bool mSupppressScrollbarUpdate:1;
+  // If true, we skipped a scrollbar layout due to mSupppressScrollbarUpdate
+  // being set at some point.  That means we should lay out scrollbars even if
+  // it might not strictly be needed next time mSupppressScrollbarUpdate is
+  // false.
+  bool mSkippedScrollbarLayout:1;
+
+  bool mHadNonInitialReflow:1;
+  // State used only by PostScrollEvents so we know
+  // which overflow states have changed.
+  bool mHorizontalOverflow:1;
+  bool mVerticalOverflow:1;
+  bool mPostedReflowCallback:1;
+  bool mMayHaveDirtyFixedChildren:1;
+  // If true, need to actually update our scrollbar attributes in the
+  // reflow callback.
+  bool mUpdateScrollbarAttributes:1;
+  // If true, we should be prepared to scroll using this scrollframe
+  // by placing descendant content into its own layer(s)
+  bool mHasBeenScrolledRecently:1;
+  // If true, the resizer is collapsed and not displayed
+  bool mCollapsedResizer:1;
+
+  // If true, the scroll frame should always be active because we always build
+  // a scrollable layer. Used for asynchronous scrolling.
+  bool mWillBuildScrollableLayer:1;
+
+  // If true, the scroll frame is an ancestor of other scrolling frames, so
+  // we shouldn't expire the displayport on this scrollframe unless those
+  // descendant scrollframes also have their displayports removed.
+  bool mIsScrollParent:1;
+
+  // Whether we are the root scroll frame that is used for containerful
+  // scrolling with a display port. If true, the scrollable frame
+  // shouldn't attach frame metrics to its layers because the container
+  // will already have the necessary frame metrics.
+  bool mIsScrollableLayerInRootContainer:1;
+
+  // If true, add clipping in ScrollFrameHelper::ComputeFrameMetrics.
+  bool mAddClipRectToLayer:1;
+
+  // True if this frame has been scrolled at least once
+  bool mHasBeenScrolled:1;
+
+  // True if the events synthesized by OSX to produce momentum scrolling should
+  // be ignored.  Reset when the next real, non-synthesized scroll event occurs.
+  bool mIgnoreMomentumScroll:1;
+
+  // True if the APZ is in the process of async-transforming this scrollframe,
+  // (as best as we can tell on the main thread, anyway).
+  bool mTransformingByAPZ:1;
+
+  // True if APZ can scroll this frame asynchronously (i.e. it has an APZC
+  // set up for this frame and it's not a scrollinfo layer).
+  bool mScrollableByAPZ:1;
+
+  // True if the APZ is allowed to zoom this scrollframe.
+  bool mZoomableByAPZ:1;
+
+  // True if we don't want the scrollbar to repaint itself right now.
+  bool mSuppressScrollbarRepaints:1;
+
+  bool mScrollsClipOnUnscrolledOutOfFlow:1;
+
+  mozilla::layout::ScrollVelocityQueue mVelocityQueue;
+
+protected:
+  class AutoScrollbarRepaintSuppression;
+  friend class AutoScrollbarRepaintSuppression;
+  class AutoScrollbarRepaintSuppression {
+  public:
+    AutoScrollbarRepaintSuppression(ScrollFrameHelper* aHelper, bool aSuppress)
+      : mHelper(aHelper)
+      , mOldSuppressValue(aHelper->mSuppressScrollbarRepaints)
+    {
+      mHelper->mSuppressScrollbarRepaints = aSuppress;
+    }
+
+    ~AutoScrollbarRepaintSuppression()
+    {
+      mHelper->mSuppressScrollbarRepaints = mOldSuppressValue;
+    }
+
+  private:
+    ScrollFrameHelper* mHelper;
+    bool mOldSuppressValue;
+  };
+
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void ScrollToWithOrigin(nsPoint aScrollPosition,
+                          nsIScrollableFrame::ScrollMode aMode,
+                          nsIAtom *aOrigin, // nullptr indicates "other" origin
+                          const nsRect* aRange,
+                          nsIScrollbarMediator::ScrollSnapMode aSnap
+                            = nsIScrollbarMediator::DISABLE_SNAP);
+
+  void CompleteAsyncScroll(const nsRect &aRange, nsIAtom* aOrigin = nullptr);
+
+  bool HasPluginFrames();
+  bool HasPerspective() const;
+  bool HasBgAttachmentLocal() const;
+  uint8_t GetScrolledFrameDir() const;
+
+  static void EnsureFrameVisPrefsCached();
+  static bool sFrameVisPrefsCached;
+  // The number of scrollports wide/high to expand when tracking frame visibility.
+  static uint32_t sHorzExpandScrollPort;
+  static uint32_t sVertExpandScrollPort;
+  // The fraction of the scrollport we allow to scroll by before we schedule
+  // an update of frame visibility.
+  static int32_t sHorzScrollFraction;
+  static int32_t sVertScrollFraction;
+};
+
+} // namespace mozilla
+
+/**
+ * The scroll frame creates and manages the scrolling view
+ *
+ * It only supports having a single child frame that typically is an area
+ * frame, but doesn't have to be. The child frame must have a view, though
+ *
+ * Scroll frames don't support incremental changes, i.e. you can't replace
+ * or remove the scrolled frame
+ */
+class nsHTMLScrollFrame : public nsContainerFrame,
+                          public nsIScrollableFrame,
+                          public nsIAnonymousContentCreator,
+                          public nsIStatefulFrame {
+public:
+  typedef mozilla::ScrollFrameHelper ScrollFrameHelper;
+  typedef mozilla::CSSIntPoint CSSIntPoint;
+  typedef mozilla::ScrollReflowInput ScrollReflowInput;
+  friend nsHTMLScrollFrame* NS_NewHTMLScrollFrame(nsIPresShell* aPresShell,
+                                                  nsStyleContext* aContext,
+                                                  bool aIsRoot);
+
+  NS_DECL_QUERYFRAME
+  NS_DECL_FRAMEARENA_HELPERS
+
+  virtual mozilla::WritingMode GetWritingMode() const override
+  {
+    if (mHelper.mScrolledFrame) {
+      return mHelper.mScrolledFrame->GetWritingMode();
+    }
+    return nsIFrame::GetWritingMode();
+  }
+
+  virtual void BuildDisplayList(nsDisplayListBuilder*   aBuilder,
+                                const nsRect&           aDirtyRect,
+                                const nsDisplayListSet& aLists) override {
+    mHelper.BuildDisplayList(aBuilder, aDirtyRect, aLists);
+  }
+
+  bool TryLayout(ScrollReflowInput* aState,
+                   ReflowOutput* aKidMetrics,
+                   bool aAssumeVScroll, bool aAssumeHScroll,
+                   bool aForce);
+  bool ScrolledContentDependsOnHeight(ScrollReflowInput* aState);
+  void ReflowScrolledFrame(ScrollReflowInput* aState,
+                           bool aAssumeHScroll,
+                           bool aAssumeVScroll,
+                           ReflowOutput* aMetrics,
+                           bool aFirstPass);
+  void ReflowContents(ScrollReflowInput* aState,
+                      const ReflowOutput& aDesiredSize);
+  void PlaceScrollArea(ScrollReflowInput& aState,
+                       const nsPoint& aScrollPosition);
+  nscoord GetIntrinsicVScrollbarWidth(nsRenderingContext *aRenderingContext);
+
+  virtual bool GetBorderRadii(const nsSize& aFrameSize, const nsSize& aBorderArea,
+                              Sides aSkipSides, nscoord aRadii[8]) const override {
+    return mHelper.GetBorderRadii(aFrameSize, aBorderArea, aSkipSides, aRadii);
+  }
+
+  virtual nscoord GetMinISize(nsRenderingContext *aRenderingContext) override;
+  virtual nscoord GetPrefISize(nsRenderingContext *aRenderingContext) override;
+  virtual nsresult GetXULPadding(nsMargin& aPadding) override;
+  virtual bool IsXULCollapsed() override;
+  
+  virtual void Reflow(nsPresContext*           aPresContext,
+                      ReflowOutput&     aDesiredSize,
+                      const ReflowInput& aReflowInput,
+                      nsReflowStatus&          aStatus) override;
+
+  virtual bool ComputeCustomOverflow(nsOverflowAreas& aOverflowAreas) override {
+    return mHelper.ComputeCustomOverflow(aOverflowAreas);
+  }
+
+  bool GetVerticalAlignBaseline(mozilla::WritingMode aWM,
+                                nscoord* aBaseline) const override {
+    *aBaseline = GetLogicalBaseline(aWM);
+    return true;
+  }
+
+  // Recomputes the scrollable overflow area we store in the helper to take children
+  // that are affected by perpsective set on the outer frame and scroll at different
+  // rates.
+  void AdjustForPerspective(nsRect& aScrollableOverflow);
+
+  // Called to set the child frames. We typically have three: the scroll area,
+  // the vertical scrollbar, and the horizontal scrollbar.
+  virtual void SetInitialChildList(ChildListID     aListID,
+                                   nsFrameList&    aChildList) override;
+  virtual void AppendFrames(ChildListID     aListID,
+                            nsFrameList&    aFrameList) override;
+  virtual void InsertFrames(ChildListID     aListID,
+                            nsIFrame*       aPrevFrame,
+                            nsFrameList&    aFrameList) override;
+  virtual void RemoveFrame(ChildListID     aListID,
+                           nsIFrame*       aOldFrame) override;
+
+  virtual void DestroyFrom(nsIFrame* aDestructRoot) override;
+
+  virtual nsIScrollableFrame* GetScrollTargetFrame() override {
+    return this;
+  }
+
+  virtual nsContainerFrame* GetContentInsertionFrame() override {
+    return mHelper.GetScrolledFrame()->GetContentInsertionFrame();
+  }
+
+  virtual bool DoesClipChildren() override { return true; }
+  virtual nsSplittableType GetSplittableType() const override;
+
+  virtual nsPoint GetPositionOfChildIgnoringScrolling(nsIFrame* aChild) override
+  { nsPoint pt = aChild->GetPosition();
+    if (aChild == mHelper.GetScrolledFrame()) pt += GetScrollPosition();
+    return pt;
+  }
+
+  // nsIAnonymousContentCreator
+  virtual nsresult CreateAnonymousContent(nsTArray<ContentInfo>& aElements) override;
+  virtual void AppendAnonymousContentTo(nsTArray<nsIContent*>& aElements,
+                                        uint32_t aFilter) override;
+
+  // nsIScrollableFrame
+  virtual nsIFrame* GetScrolledFrame() const override {
+    return mHelper.GetScrolledFrame();
+  }
+  virtual mozilla::ScrollbarStyles GetScrollbarStyles() const override {
+    return mHelper.GetScrollbarStylesFromFrame();
+  }
+  virtual uint32_t GetScrollbarVisibility() const override {
+    return mHelper.GetScrollbarVisibility();
+  }
+  virtual nsMargin GetActualScrollbarSizes() const override {
+    return mHelper.GetActualScrollbarSizes();
+  }
+  virtual nsMargin GetDesiredScrollbarSizes(nsBoxLayoutState* aState) override {
+    return mHelper.GetDesiredScrollbarSizes(aState);
+  }
+  virtual nsMargin GetDesiredScrollbarSizes(nsPresContext* aPresContext,
+          nsRenderingContext* aRC) override {
+    nsBoxLayoutState bls(aPresContext, aRC, 0);
+    return GetDesiredScrollbarSizes(&bls);
+  }
+  virtual nscoord GetNondisappearingScrollbarWidth(nsPresContext* aPresContext,
+          nsRenderingContext* aRC, mozilla::WritingMode aWM) override {
+    nsBoxLayoutState bls(aPresContext, aRC, 0);
+    return mHelper.GetNondisappearingScrollbarWidth(&bls, aWM);
+  }
+  virtual nsRect GetScrolledRect() const override {
+    return mHelper.GetScrolledRect();
+  }
+  virtual nsRect GetScrollPortRect() const override {
+    return mHelper.GetScrollPortRect();
+  }
+  virtual nsPoint GetScrollPosition() const override {
+    return mHelper.GetScrollPosition();
+  }
+  virtual nsPoint GetLogicalScrollPosition() const override {
+    return mHelper.GetLogicalScrollPosition();
+  }
+  virtual nsRect GetScrollRange() const override {
+    return mHelper.GetScrollRange();
+  }
+  virtual nsSize GetScrollPositionClampingScrollPortSize() const override {
+    return mHelper.GetScrollPositionClampingScrollPortSize();
+  }
+  virtual nsSize GetLineScrollAmount() const override {
+    return mHelper.GetLineScrollAmount();
+  }
+  virtual nsSize GetPageScrollAmount() const override {
+    return mHelper.GetPageScrollAmount();
+  }
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  virtual void ScrollTo(nsPoint aScrollPosition, ScrollMode aMode,
+                        const nsRect* aRange = nullptr,
+                        nsIScrollbarMediator::ScrollSnapMode aSnap
+                          = nsIScrollbarMediator::DISABLE_SNAP)
+                        override {
+    mHelper.ScrollTo(aScrollPosition, aMode, aRange, aSnap);
+  }
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  virtual void ScrollToCSSPixels(const CSSIntPoint& aScrollPosition,
+                                 nsIScrollableFrame::ScrollMode aMode
+                                   = nsIScrollableFrame::INSTANT) override {
+    mHelper.ScrollToCSSPixels(aScrollPosition, aMode);
+  }
+  virtual void ScrollToCSSPixelsApproximate(const mozilla::CSSPoint& aScrollPosition,
+                                            nsIAtom* aOrigin = nullptr) override {
+    mHelper.ScrollToCSSPixelsApproximate(aScrollPosition, aOrigin);
+  }
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  virtual CSSIntPoint GetScrollPositionCSSPixels() override {
+    return mHelper.GetScrollPositionCSSPixels();
+  }
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  virtual void ScrollBy(nsIntPoint aDelta, ScrollUnit aUnit, ScrollMode aMode,
+                        nsIntPoint* aOverflow, nsIAtom* aOrigin = nullptr,
+                        nsIScrollableFrame::ScrollMomentum aMomentum = nsIScrollableFrame::NOT_MOMENTUM,
+                        nsIScrollbarMediator::ScrollSnapMode aSnap
+                          = nsIScrollbarMediator::DISABLE_SNAP)
+                        override {
+    mHelper.ScrollBy(aDelta, aUnit, aMode, aOverflow, aOrigin, aMomentum, aSnap);
+  }
+  virtual void ScrollSnap() override {
+    mHelper.ScrollSnap();
+  }
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  virtual void ScrollToRestoredPosition() override {
+    mHelper.ScrollToRestoredPosition();
+  }
+  virtual void AddScrollPositionListener(nsIScrollPositionListener* aListener) override {
+    mHelper.AddScrollPositionListener(aListener);
+  }
+  virtual void RemoveScrollPositionListener(nsIScrollPositionListener* aListener) override {
+    mHelper.RemoveScrollPositionListener(aListener);
+  }
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  virtual void CurPosAttributeChanged(nsIContent* aChild) override {
+    mHelper.CurPosAttributeChanged(aChild);
+  }
+  NS_IMETHOD PostScrolledAreaEventForCurrentArea() override {
+    mHelper.PostScrolledAreaEvent();
+    return NS_OK;
+  }
+  virtual bool IsScrollingActive(nsDisplayListBuilder* aBuilder) override {
+    return mHelper.IsScrollingActive(aBuilder);
+  }
+  virtual bool IsProcessingAsyncScroll() override {
+    return mHelper.IsProcessingAsyncScroll();
+  }
+  virtual void ResetScrollPositionForLayerPixelAlignment() override {
+    mHelper.ResetScrollPositionForLayerPixelAlignment();
+  }
+  virtual bool DidHistoryRestore() const override {
+    return mHelper.mDidHistoryRestore;
+  }
+  virtual void ClearDidHistoryRestore() override {
+    mHelper.mDidHistoryRestore = false;
+  }
+  virtual bool IsRectNearlyVisible(const nsRect& aRect) override {
+    return mHelper.IsRectNearlyVisible(aRect);
+  }
+  virtual nsRect ExpandRectToNearlyVisible(const nsRect& aRect) const override {
+    return mHelper.ExpandRectToNearlyVisible(aRect);
+  }
+  virtual nsIAtom* LastScrollOrigin() override {
+    return mHelper.LastScrollOrigin();
+  }
+  virtual void AllowScrollOriginDowngrade() override {
+    mHelper.AllowScrollOriginDowngrade();
+  }
+  virtual nsIAtom* LastSmoothScrollOrigin() override {
+    return mHelper.LastSmoothScrollOrigin();
+  }
+  virtual uint32_t CurrentScrollGeneration() override {
+    return mHelper.CurrentScrollGeneration();
+  }
+  virtual nsPoint LastScrollDestination() override {
+    return mHelper.LastScrollDestination();
+  }
+  virtual void ResetScrollInfoIfGeneration(uint32_t aGeneration) override {
+    mHelper.ResetScrollInfoIfGeneration(aGeneration);
+  }
+  virtual bool WantAsyncScroll() const override {
+    return mHelper.WantAsyncScroll();
+  }
+  virtual mozilla::Maybe<mozilla::layers::ScrollMetadata> ComputeScrollMetadata(
+    Layer* aLayer, nsIFrame* aContainerReferenceFrame,
+    const ContainerLayerParameters& aParameters,
+    const mozilla::DisplayItemClip* aClip) const override
+  {
+    return mHelper.ComputeScrollMetadata(aLayer, aContainerReferenceFrame, aParameters, aClip);
+  }
+  virtual bool IsIgnoringViewportClipping() const override {
+    return mHelper.IsIgnoringViewportClipping();
+  }
+  virtual void MarkScrollbarsDirtyForReflow() const override {
+    mHelper.MarkScrollbarsDirtyForReflow();
+  }
+  virtual bool UsesContainerScrolling() const override {
+    return mHelper.UsesContainerScrolling();
+  }
+  virtual bool DecideScrollableLayer(nsDisplayListBuilder* aBuilder,
+                                     nsRect* aDirtyRect,
+                                     bool aAllowCreateDisplayPort) override {
+    return mHelper.DecideScrollableLayer(aBuilder, aDirtyRect, aAllowCreateDisplayPort);
+  }
+  virtual void NotifyApproximateFrameVisibilityUpdate() override {
+    mHelper.NotifyApproximateFrameVisibilityUpdate();
+  }
+  virtual bool GetDisplayPortAtLastApproximateFrameVisibilityUpdate(nsRect* aDisplayPort) override {
+    return mHelper.GetDisplayPortAtLastApproximateFrameVisibilityUpdate(aDisplayPort);
+  }
+  void TriggerDisplayPortExpiration() override {
+    mHelper.TriggerDisplayPortExpiration();
+  }
+
+  // nsIStatefulFrame
+  NS_IMETHOD SaveState(nsPresState** aState) override {
+    NS_ENSURE_ARG_POINTER(aState);
+    *aState = mHelper.SaveState();
+    return NS_OK;
+  }
+  NS_IMETHOD RestoreState(nsPresState* aState) override {
+    NS_ENSURE_ARG_POINTER(aState);
+    mHelper.RestoreState(aState);
+    return NS_OK;
+  }
+
+  /**
+   * Get the "type" of the frame
+   *
+   * @see nsGkAtoms::scrollFrame
+   */
+  virtual nsIAtom* GetType() const override;
+
+  // nsIScrollbarMediator
+  virtual void ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                            nsIScrollbarMediator::ScrollSnapMode aSnap
+                              = nsIScrollbarMediator::DISABLE_SNAP) override {
+    mHelper.ScrollByPage(aScrollbar, aDirection, aSnap);
+  }
+  virtual void ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                             nsIScrollbarMediator::ScrollSnapMode aSnap
+                               = nsIScrollbarMediator::DISABLE_SNAP) override {
+    mHelper.ScrollByWhole(aScrollbar, aDirection, aSnap);
+  }
+  virtual void ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                            nsIScrollbarMediator::ScrollSnapMode aSnap
+                              = nsIScrollbarMediator::DISABLE_SNAP) override {
+    mHelper.ScrollByLine(aScrollbar, aDirection, aSnap);
+  }
+  virtual void RepeatButtonScroll(nsScrollbarFrame* aScrollbar) override {
+    mHelper.RepeatButtonScroll(aScrollbar);
+  }
+  virtual void ThumbMoved(nsScrollbarFrame* aScrollbar,
+                          nscoord aOldPos,
+                          nscoord aNewPos) override {
+    mHelper.ThumbMoved(aScrollbar, aOldPos, aNewPos);
+  }
+  virtual void ScrollbarReleased(nsScrollbarFrame* aScrollbar) override {
+    mHelper.ScrollbarReleased(aScrollbar);
+  }
+  virtual void VisibilityChanged(bool aVisible) override {}
+  virtual nsIFrame* GetScrollbarBox(bool aVertical) override {
+    return mHelper.GetScrollbarBox(aVertical);
+  }
+  virtual void ScrollbarActivityStarted() const override;
+  virtual void ScrollbarActivityStopped() const override;
+
+  virtual bool IsScrollbarOnRight() const override {
+    return mHelper.IsScrollbarOnRight();
+  }
+
+  virtual bool ShouldSuppressScrollbarRepaints() const override {
+    return mHelper.ShouldSuppressScrollbarRepaints();
+  }
+
+  virtual void SetTransformingByAPZ(bool aTransforming) override {
+    mHelper.SetTransformingByAPZ(aTransforming);
+  }
+  bool IsTransformingByAPZ() const override {
+    return mHelper.IsTransformingByAPZ();
+  }
+  void SetScrollableByAPZ(bool aScrollable) override {
+    mHelper.SetScrollableByAPZ(aScrollable);
+  }
+  void SetZoomableByAPZ(bool aZoomable) override {
+    mHelper.SetZoomableByAPZ(aZoomable);
+  }
+  void SetScrollsClipOnUnscrolledOutOfFlow() override {
+    mHelper.SetScrollsClipOnUnscrolledOutOfFlow();
+  }
+  
+  ScrollSnapInfo GetScrollSnapInfo() const override {
+    return mHelper.GetScrollSnapInfo();
+  }
+
+#ifdef DEBUG_FRAME_DUMP
+  virtual nsresult GetFrameName(nsAString& aResult) const override;
+#endif
+
+#ifdef ACCESSIBILITY
+  virtual mozilla::a11y::AccType AccessibleType() override;
+#endif
+
+protected:
+  nsHTMLScrollFrame(nsStyleContext* aContext, bool aIsRoot);
+  void SetSuppressScrollbarUpdate(bool aSuppress) {
+    mHelper.mSupppressScrollbarUpdate = aSuppress;
+  }
+  bool GuessHScrollbarNeeded(const ScrollReflowInput& aState);
+  bool GuessVScrollbarNeeded(const ScrollReflowInput& aState);
+
+  bool IsScrollbarUpdateSuppressed() const {
+    return mHelper.mSupppressScrollbarUpdate;
+  }
+
+  // Return whether we're in an "initial" reflow.  Some reflows with
+  // NS_FRAME_FIRST_REFLOW set are NOT "initial" as far as we're concerned.
+  bool InInitialReflow() const;
+  
+  /**
+   * Override this to return false if computed bsize/min-bsize/max-bsize
+   * should NOT be propagated to child content.
+   * nsListControlFrame uses this.
+   */
+  virtual bool ShouldPropagateComputedBSizeToScrolledContent() const { return true; }
+
+private:
+  friend class mozilla::ScrollFrameHelper;
+  ScrollFrameHelper mHelper;
+};
+
+/**
+ * The scroll frame creates and manages the scrolling view
+ *
+ * It only supports having a single child frame that typically is an area
+ * frame, but doesn't have to be. The child frame must have a view, though
+ *
+ * Scroll frames don't support incremental changes, i.e. you can't replace
+ * or remove the scrolled frame
+ */
+class nsXULScrollFrame final : public nsBoxFrame,
+                               public nsIScrollableFrame,
+                               public nsIAnonymousContentCreator,
+                               public nsIStatefulFrame
+{
+public:
+  typedef mozilla::ScrollFrameHelper ScrollFrameHelper;
+  typedef mozilla::CSSIntPoint CSSIntPoint;
+
+  NS_DECL_QUERYFRAME
+  NS_DECL_FRAMEARENA_HELPERS
+
+  friend nsXULScrollFrame* NS_NewXULScrollFrame(nsIPresShell* aPresShell,
+                                                nsStyleContext* aContext,
+                                                bool aIsRoot,
+                                                bool aClipAllDescendants);
+
+  virtual void BuildDisplayList(nsDisplayListBuilder*   aBuilder,
+                                const nsRect&           aDirtyRect,
+                                const nsDisplayListSet& aLists) override {
+    mHelper.BuildDisplayList(aBuilder, aDirtyRect, aLists);
+  }
+
+  // XXXldb Is this actually used?
+#if 0
+  virtual nscoord GetMinISize(nsRenderingContext *aRenderingContext) override;
+#endif
+
+  virtual bool ComputeCustomOverflow(nsOverflowAreas& aOverflowAreas) override {
+    return mHelper.ComputeCustomOverflow(aOverflowAreas);
+  }
+
+  bool GetVerticalAlignBaseline(mozilla::WritingMode aWM,
+                                nscoord* aBaseline) const override {
+    *aBaseline = GetLogicalBaseline(aWM);
+    return true;
+  }
+
+  // Called to set the child frames. We typically have three: the scroll area,
+  // the vertical scrollbar, and the horizontal scrollbar.
+  virtual void SetInitialChildList(ChildListID     aListID,
+                                   nsFrameList&    aChildList) override;
+  virtual void AppendFrames(ChildListID     aListID,
+                            nsFrameList&    aFrameList) override;
+  virtual void InsertFrames(ChildListID     aListID,
+                            nsIFrame*       aPrevFrame,
+                            nsFrameList&    aFrameList) override;
+  virtual void RemoveFrame(ChildListID     aListID,
+                           nsIFrame*       aOldFrame) override;
+
+  virtual void DestroyFrom(nsIFrame* aDestructRoot) override;
+
+
+  virtual nsIScrollableFrame* GetScrollTargetFrame() override {
+    return this;
+  }
+
+  virtual nsContainerFrame* GetContentInsertionFrame() override {
+    return mHelper.GetScrolledFrame()->GetContentInsertionFrame();
+  }
+
+  virtual bool DoesClipChildren() override { return true; }
+  virtual nsSplittableType GetSplittableType() const override;
+
+  virtual nsPoint GetPositionOfChildIgnoringScrolling(nsIFrame* aChild) override
+  { nsPoint pt = aChild->GetPosition();
+    if (aChild == mHelper.GetScrolledFrame())
+      pt += mHelper.GetLogicalScrollPosition();
+    return pt;
+  }
+
+  // nsIAnonymousContentCreator
+  virtual nsresult CreateAnonymousContent(nsTArray<ContentInfo>& aElements) override;
+  virtual void AppendAnonymousContentTo(nsTArray<nsIContent*>& aElements,
+                                        uint32_t aFilter) override;
+
+  virtual nsSize GetXULMinSize(nsBoxLayoutState& aBoxLayoutState) override;
+  virtual nsSize GetXULPrefSize(nsBoxLayoutState& aBoxLayoutState) override;
+  virtual nsSize GetXULMaxSize(nsBoxLayoutState& aBoxLayoutState) override;
+  virtual nscoord GetXULBoxAscent(nsBoxLayoutState& aBoxLayoutState) override;
+
+  NS_IMETHOD DoXULLayout(nsBoxLayoutState& aBoxLayoutState) override;
+  virtual nsresult GetXULPadding(nsMargin& aPadding) override;
+
+  virtual bool GetBorderRadii(const nsSize& aFrameSize, const nsSize& aBorderArea,
+                              Sides aSkipSides, nscoord aRadii[8]) const override {
+    return mHelper.GetBorderRadii(aFrameSize, aBorderArea, aSkipSides, aRadii);
+  }
+
+  nsresult XULLayout(nsBoxLayoutState& aState);
+  void LayoutScrollArea(nsBoxLayoutState& aState, const nsPoint& aScrollPosition);
+
+  static bool AddRemoveScrollbar(bool& aHasScrollbar, 
+                                   nscoord& aXY, 
+                                   nscoord& aSize, 
+                                   nscoord aSbSize, 
+                                   bool aOnRightOrBottom, 
+                                   bool aAdd);
+  
+  bool AddRemoveScrollbar(nsBoxLayoutState& aState, 
+                            bool aOnRightOrBottom, 
+                            bool aHorizontal, 
+                            bool aAdd);
+  
+  bool AddHorizontalScrollbar (nsBoxLayoutState& aState, bool aOnBottom);
+  bool AddVerticalScrollbar   (nsBoxLayoutState& aState, bool aOnRight);
+  void RemoveHorizontalScrollbar(nsBoxLayoutState& aState, bool aOnBottom);
+  void RemoveVerticalScrollbar  (nsBoxLayoutState& aState, bool aOnRight);
+
+  static void AdjustReflowInputForPrintPreview(nsBoxLayoutState& aState, bool& aSetBack);
+  static void AdjustReflowInputBack(nsBoxLayoutState& aState, bool aSetBack);
+
+  // nsIScrollableFrame
+  virtual nsIFrame* GetScrolledFrame() const override {
+    return mHelper.GetScrolledFrame();
+  }
+  virtual mozilla::ScrollbarStyles GetScrollbarStyles() const override {
+    return mHelper.GetScrollbarStylesFromFrame();
+  }
+  virtual uint32_t GetScrollbarVisibility() const override {
+    return mHelper.GetScrollbarVisibility();
+  }
+  virtual nsMargin GetActualScrollbarSizes() const override {
+    return mHelper.GetActualScrollbarSizes();
+  }
+  virtual nsMargin GetDesiredScrollbarSizes(nsBoxLayoutState* aState) override {
+    return mHelper.GetDesiredScrollbarSizes(aState);
+  }
+  virtual nsMargin GetDesiredScrollbarSizes(nsPresContext* aPresContext,
+          nsRenderingContext* aRC) override {
+    nsBoxLayoutState bls(aPresContext, aRC, 0);
+    return GetDesiredScrollbarSizes(&bls);
+  }
+  virtual nscoord GetNondisappearingScrollbarWidth(nsPresContext* aPresContext,
+          nsRenderingContext* aRC, mozilla::WritingMode aWM) override {
+    nsBoxLayoutState bls(aPresContext, aRC, 0);
+    return mHelper.GetNondisappearingScrollbarWidth(&bls, aWM);
+  }
+  virtual nsRect GetScrolledRect() const override {
+    return mHelper.GetScrolledRect();
+  }
+  virtual nsRect GetScrollPortRect() const override {
+    return mHelper.GetScrollPortRect();
+  }
+  virtual nsPoint GetScrollPosition() const override {
+    return mHelper.GetScrollPosition();
+  }
+  virtual nsPoint GetLogicalScrollPosition() const override {
+    return mHelper.GetLogicalScrollPosition();
+  }
+  virtual nsRect GetScrollRange() const override {
+    return mHelper.GetScrollRange();
+  }
+  virtual nsSize GetScrollPositionClampingScrollPortSize() const override {
+    return mHelper.GetScrollPositionClampingScrollPortSize();
+  }
+  virtual nsSize GetLineScrollAmount() const override {
+    return mHelper.GetLineScrollAmount();
+  }
+  virtual nsSize GetPageScrollAmount() const override {
+    return mHelper.GetPageScrollAmount();
+  }
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  virtual void ScrollTo(nsPoint aScrollPosition, ScrollMode aMode,
+                        const nsRect* aRange = nullptr,
+                        ScrollSnapMode aSnap = nsIScrollbarMediator::DISABLE_SNAP)
+                        override {
+    mHelper.ScrollTo(aScrollPosition, aMode, aRange, aSnap);
+  }
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  virtual void ScrollToCSSPixels(const CSSIntPoint& aScrollPosition,
+                                 nsIScrollableFrame::ScrollMode aMode
+                                   = nsIScrollableFrame::INSTANT) override {
+    mHelper.ScrollToCSSPixels(aScrollPosition, aMode);
+  }
+  virtual void ScrollToCSSPixelsApproximate(const mozilla::CSSPoint& aScrollPosition,
+                                            nsIAtom* aOrigin = nullptr) override {
+    mHelper.ScrollToCSSPixelsApproximate(aScrollPosition, aOrigin);
+  }
+  virtual CSSIntPoint GetScrollPositionCSSPixels() override {
+    return mHelper.GetScrollPositionCSSPixels();
+  }
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  virtual void ScrollBy(nsIntPoint aDelta, ScrollUnit aUnit, ScrollMode aMode,
+                        nsIntPoint* aOverflow, nsIAtom* aOrigin = nullptr,
+                        nsIScrollableFrame::ScrollMomentum aMomentum = nsIScrollableFrame::NOT_MOMENTUM,
+                        nsIScrollbarMediator::ScrollSnapMode aSnap
+                          = nsIScrollbarMediator::DISABLE_SNAP)
+                        override {
+    mHelper.ScrollBy(aDelta, aUnit, aMode, aOverflow, aOrigin, aMomentum, aSnap);
+  }
+  virtual void ScrollSnap() override {
+    mHelper.ScrollSnap();
+  }
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  virtual void ScrollToRestoredPosition() override {
+    mHelper.ScrollToRestoredPosition();
+  }
+  virtual void AddScrollPositionListener(nsIScrollPositionListener* aListener) override {
+    mHelper.AddScrollPositionListener(aListener);
+  }
+  virtual void RemoveScrollPositionListener(nsIScrollPositionListener* aListener) override {
+    mHelper.RemoveScrollPositionListener(aListener);
+  }
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  virtual void CurPosAttributeChanged(nsIContent* aChild) override {
+    mHelper.CurPosAttributeChanged(aChild);
+  }
+  NS_IMETHOD PostScrolledAreaEventForCurrentArea() override {
+    mHelper.PostScrolledAreaEvent();
+    return NS_OK;
+  }
+  virtual bool IsScrollingActive(nsDisplayListBuilder* aBuilder) override {
+    return mHelper.IsScrollingActive(aBuilder);
+  }
+  virtual bool IsProcessingAsyncScroll() override {
+    return mHelper.IsProcessingAsyncScroll();
+  }
+  virtual void ResetScrollPositionForLayerPixelAlignment() override {
+    mHelper.ResetScrollPositionForLayerPixelAlignment();
+  }
+  virtual bool DidHistoryRestore() const override {
+    return mHelper.mDidHistoryRestore;
+  }
+  virtual void ClearDidHistoryRestore() override {
+    mHelper.mDidHistoryRestore = false;
+  }
+  virtual bool IsRectNearlyVisible(const nsRect& aRect) override {
+    return mHelper.IsRectNearlyVisible(aRect);
+  }
+  virtual nsRect ExpandRectToNearlyVisible(const nsRect& aRect) const override {
+    return mHelper.ExpandRectToNearlyVisible(aRect);
+  }
+  virtual nsIAtom* LastScrollOrigin() override {
+    return mHelper.LastScrollOrigin();
+  }
+  virtual void AllowScrollOriginDowngrade() override {
+    mHelper.AllowScrollOriginDowngrade();
+  }
+  virtual nsIAtom* LastSmoothScrollOrigin() override {
+    return mHelper.LastSmoothScrollOrigin();
+  }
+  virtual uint32_t CurrentScrollGeneration() override {
+    return mHelper.CurrentScrollGeneration();
+  }
+  virtual nsPoint LastScrollDestination() override {
+    return mHelper.LastScrollDestination();
+  }
+  virtual void ResetScrollInfoIfGeneration(uint32_t aGeneration) override {
+    mHelper.ResetScrollInfoIfGeneration(aGeneration);
+  }
+  virtual bool WantAsyncScroll() const override {
+    return mHelper.WantAsyncScroll();
+  }
+  virtual mozilla::Maybe<mozilla::layers::ScrollMetadata> ComputeScrollMetadata(
+    Layer* aLayer, nsIFrame* aContainerReferenceFrame,
+    const ContainerLayerParameters& aParameters,
+    const mozilla::DisplayItemClip* aClip) const override
+  {
+    return mHelper.ComputeScrollMetadata(aLayer, aContainerReferenceFrame, aParameters, aClip);
+  }
+  virtual bool IsIgnoringViewportClipping() const override {
+    return mHelper.IsIgnoringViewportClipping();
+  }
+  virtual void MarkScrollbarsDirtyForReflow() const override {
+    mHelper.MarkScrollbarsDirtyForReflow();
+  }
+
+  // nsIStatefulFrame
+  NS_IMETHOD SaveState(nsPresState** aState) override {
+    NS_ENSURE_ARG_POINTER(aState);
+    *aState = mHelper.SaveState();
+    return NS_OK;
+  }
+  NS_IMETHOD RestoreState(nsPresState* aState) override {
+    NS_ENSURE_ARG_POINTER(aState);
+    mHelper.RestoreState(aState);
+    return NS_OK;
+  }
+
+  /**
+   * Get the "type" of the frame
+   *
+   * @see nsGkAtoms::scrollFrame
+   */
+  virtual nsIAtom* GetType() const override;
+  
+  virtual bool IsFrameOfType(uint32_t aFlags) const override
+  {
+    // Override bogus IsFrameOfType in nsBoxFrame.
+    if (aFlags & (nsIFrame::eReplacedContainsBlock | nsIFrame::eReplaced))
+      return false;
+    return nsBoxFrame::IsFrameOfType(aFlags);
+  }
+
+  virtual void ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                            nsIScrollbarMediator::ScrollSnapMode aSnap
+                              = nsIScrollbarMediator::DISABLE_SNAP) override {
+    mHelper.ScrollByPage(aScrollbar, aDirection, aSnap);
+  }
+  virtual void ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                             nsIScrollbarMediator::ScrollSnapMode aSnap
+                               = nsIScrollbarMediator::DISABLE_SNAP) override {
+    mHelper.ScrollByWhole(aScrollbar, aDirection, aSnap);
+  }
+  virtual void ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                            nsIScrollbarMediator::ScrollSnapMode aSnap
+                              = nsIScrollbarMediator::DISABLE_SNAP) override {
+    mHelper.ScrollByLine(aScrollbar, aDirection, aSnap);
+  }
+  virtual void RepeatButtonScroll(nsScrollbarFrame* aScrollbar) override {
+    mHelper.RepeatButtonScroll(aScrollbar);
+  }
+  virtual void ThumbMoved(nsScrollbarFrame* aScrollbar,
+                          nscoord aOldPos,
+                          nscoord aNewPos) override {
+    mHelper.ThumbMoved(aScrollbar, aOldPos, aNewPos);
+  }
+  virtual void ScrollbarReleased(nsScrollbarFrame* aScrollbar) override {
+    mHelper.ScrollbarReleased(aScrollbar);
+  }
+  virtual void VisibilityChanged(bool aVisible) override {}
+  virtual nsIFrame* GetScrollbarBox(bool aVertical) override {
+    return mHelper.GetScrollbarBox(aVertical);
+  }
+
+  virtual void ScrollbarActivityStarted() const override;
+  virtual void ScrollbarActivityStopped() const override;
+
+  virtual bool IsScrollbarOnRight() const override {
+    return mHelper.IsScrollbarOnRight();
+  }
+
+  virtual bool ShouldSuppressScrollbarRepaints() const override {
+    return mHelper.ShouldSuppressScrollbarRepaints();
+  }
+
+  virtual void SetTransformingByAPZ(bool aTransforming) override {
+    mHelper.SetTransformingByAPZ(aTransforming);
+  }
+  virtual bool UsesContainerScrolling() const override {
+    return mHelper.UsesContainerScrolling();
+  }
+  bool IsTransformingByAPZ() const override {
+    return mHelper.IsTransformingByAPZ();
+  }
+  void SetScrollableByAPZ(bool aScrollable) override {
+    mHelper.SetScrollableByAPZ(aScrollable);
+  }
+  void SetZoomableByAPZ(bool aZoomable) override {
+    mHelper.SetZoomableByAPZ(aZoomable);
+  }
+  void SetScrollsClipOnUnscrolledOutOfFlow() override {
+    mHelper.SetScrollsClipOnUnscrolledOutOfFlow();
+  }
+  virtual bool DecideScrollableLayer(nsDisplayListBuilder* aBuilder,
+                                     nsRect* aDirtyRect,
+                                     bool aAllowCreateDisplayPort) override {
+    return mHelper.DecideScrollableLayer(aBuilder, aDirtyRect, aAllowCreateDisplayPort);
+  }
+  virtual void NotifyApproximateFrameVisibilityUpdate() override {
+    mHelper.NotifyApproximateFrameVisibilityUpdate();
+  }
+  virtual bool GetDisplayPortAtLastApproximateFrameVisibilityUpdate(nsRect* aDisplayPort) override {
+    return mHelper.GetDisplayPortAtLastApproximateFrameVisibilityUpdate(aDisplayPort);
+  }
+  void TriggerDisplayPortExpiration() override {
+    mHelper.TriggerDisplayPortExpiration();
+  }
+
+  ScrollSnapInfo GetScrollSnapInfo() const override {
+    return mHelper.GetScrollSnapInfo();
+  }
+
+#ifdef DEBUG_FRAME_DUMP
+  virtual nsresult GetFrameName(nsAString& aResult) const override;
+#endif
+
+protected:
+  nsXULScrollFrame(nsStyleContext* aContext, bool aIsRoot,
+                   bool aClipAllDescendants);
+
+  void ClampAndSetBounds(nsBoxLayoutState& aState, 
+                         nsRect& aRect,
+                         nsPoint aScrollPosition,
+                         bool aRemoveOverflowAreas = false) {
+    /* 
+     * For RTL frames, restore the original scrolled position of the right
+     * edge, then subtract the current width to find the physical position.
+     */
+    if (!mHelper.IsPhysicalLTR()) {
+      aRect.x = mHelper.mScrollPort.XMost() - aScrollPosition.x - aRect.width;
+    }
+    mHelper.mScrolledFrame->SetXULBounds(aState, aRect, aRemoveOverflowAreas);
+  }
+
+private:
+  friend class mozilla::ScrollFrameHelper;
+  ScrollFrameHelper mHelper;
+};
+
+#endif /* nsGfxScrollFrame_h___ */