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diff --git a/image/decoders/nsGIFDecoder2.h b/image/decoders/nsGIFDecoder2.h
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+/* -*- 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 mozilla_image_decoders_nsGIFDecoder2_h
+#define mozilla_image_decoders_nsGIFDecoder2_h
+
+#include "Decoder.h"
+#include "GIF2.h"
+#include "StreamingLexer.h"
+#include "SurfacePipe.h"
+
+namespace mozilla {
+namespace image {
+class RasterImage;
+
+//////////////////////////////////////////////////////////////////////
+// nsGIFDecoder2 Definition
+
+class nsGIFDecoder2 : public Decoder
+{
+public:
+  ~nsGIFDecoder2();
+
+protected:
+  LexerResult DoDecode(SourceBufferIterator& aIterator,
+                       IResumable* aOnResume) override;
+  nsresult FinishInternal() override;
+
+  Maybe<Telemetry::ID> SpeedHistogram() const override;
+
+private:
+  friend class DecoderFactory;
+
+  // Decoders should only be instantiated via DecoderFactory.
+  explicit nsGIFDecoder2(RasterImage* aImage);
+
+  /// Called when we begin decoding the image.
+  void      BeginGIF();
+
+  /**
+   * Called when we begin decoding a frame.
+   *
+   * @param aFrameRect The region of the image that contains data. The region
+   *                   outside this rect is transparent.
+   * @param aDepth The palette depth of this frame.
+   * @param aIsInterlaced If true, this frame is an interlaced frame.
+   */
+  nsresult  BeginImageFrame(const gfx::IntRect& aFrameRect,
+                            uint16_t aDepth,
+                            bool aIsInterlaced);
+
+  /// Called when we finish decoding a frame.
+  void      EndImageFrame();
+
+  /// Called when we finish decoding the entire image.
+  void      FlushImageData();
+
+  /// Transforms a palette index into a pixel.
+  template <typename PixelSize> PixelSize
+  ColormapIndexToPixel(uint8_t aIndex);
+
+  /// A generator function that performs LZW decompression and yields pixels.
+  template <typename PixelSize> NextPixel<PixelSize>
+  YieldPixel(const uint8_t* aData, size_t aLength, size_t* aBytesReadOut);
+
+  /// Checks if we have transparency, either because the header indicates that
+  /// there's alpha, or because the frame rect doesn't cover the entire image.
+  bool CheckForTransparency(const gfx::IntRect& aFrameRect);
+
+  // @return the clear code used for LZW decompression.
+  int ClearCode() const { return 1 << mGIFStruct.datasize; }
+
+  enum class State
+  {
+    FAILURE,
+    SUCCESS,
+    GIF_HEADER,
+    SCREEN_DESCRIPTOR,
+    GLOBAL_COLOR_TABLE,
+    FINISHED_GLOBAL_COLOR_TABLE,
+    BLOCK_HEADER,
+    EXTENSION_HEADER,
+    GRAPHIC_CONTROL_EXTENSION,
+    APPLICATION_IDENTIFIER,
+    NETSCAPE_EXTENSION_SUB_BLOCK,
+    NETSCAPE_EXTENSION_DATA,
+    IMAGE_DESCRIPTOR,
+    FINISH_IMAGE_DESCRIPTOR,
+    LOCAL_COLOR_TABLE,
+    FINISHED_LOCAL_COLOR_TABLE,
+    IMAGE_DATA_BLOCK,
+    IMAGE_DATA_SUB_BLOCK,
+    LZW_DATA,
+    SKIP_LZW_DATA,
+    FINISHED_LZW_DATA,
+    SKIP_SUB_BLOCKS,
+    SKIP_DATA_THEN_SKIP_SUB_BLOCKS,
+    FINISHED_SKIPPING_DATA
+  };
+
+  LexerTransition<State> ReadGIFHeader(const char* aData);
+  LexerTransition<State> ReadScreenDescriptor(const char* aData);
+  LexerTransition<State> ReadGlobalColorTable(const char* aData, size_t aLength);
+  LexerTransition<State> FinishedGlobalColorTable();
+  LexerTransition<State> ReadBlockHeader(const char* aData);
+  LexerTransition<State> ReadExtensionHeader(const char* aData);
+  LexerTransition<State> ReadGraphicControlExtension(const char* aData);
+  LexerTransition<State> ReadApplicationIdentifier(const char* aData);
+  LexerTransition<State> ReadNetscapeExtensionSubBlock(const char* aData);
+  LexerTransition<State> ReadNetscapeExtensionData(const char* aData);
+  LexerTransition<State> ReadImageDescriptor(const char* aData);
+  LexerTransition<State> FinishImageDescriptor(const char* aData);
+  LexerTransition<State> ReadLocalColorTable(const char* aData, size_t aLength);
+  LexerTransition<State> FinishedLocalColorTable();
+  LexerTransition<State> ReadImageDataBlock(const char* aData);
+  LexerTransition<State> ReadImageDataSubBlock(const char* aData);
+  LexerTransition<State> ReadLZWData(const char* aData, size_t aLength);
+  LexerTransition<State> SkipSubBlocks(const char* aData);
+
+  // The StreamingLexer used to manage input. The initial size of the buffer is
+  // chosen as a little larger than the maximum size of any fixed-length data we
+  // have to read for a state. We read variable-length data in unbuffered mode
+  // so the buffer shouldn't have to be resized during decoding.
+  StreamingLexer<State, 16> mLexer;
+
+  uint32_t mOldColor;        // The old value of the transparent pixel
+
+  // The frame number of the currently-decoding frame when we're in the middle
+  // of decoding it, and -1 otherwise.
+  int32_t mCurrentFrameIndex;
+
+  // When we're reading in the global or local color table, this records our
+  // current position - i.e., the offset into which the next byte should be
+  // written.
+  size_t mColorTablePos;
+
+  uint8_t mColorMask;        // Apply this to the pixel to keep within colormap
+  bool mGIFOpen;
+  bool mSawTransparency;
+
+  gif_struct mGIFStruct;
+
+  SurfacePipe mPipe;  /// The SurfacePipe used to write to the output surface.
+};
+
+} // namespace image
+} // namespace mozilla
+
+#endif // mozilla_image_decoders_nsGIFDecoder2_h