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diff --git a/image/decoders/nsICODecoder.h b/image/decoders/nsICODecoder.h
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+++ b/image/decoders/nsICODecoder.h
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+/* vim:set tw=80 expandtab softtabstop=4 ts=4 sw=4: */
+/* 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_nsICODecoder_h
+#define mozilla_image_decoders_nsICODecoder_h
+
+#include "StreamingLexer.h"
+#include "Decoder.h"
+#include "imgFrame.h"
+#include "mozilla/gfx/2D.h"
+#include "nsBMPDecoder.h"
+#include "nsPNGDecoder.h"
+#include "ICOFileHeaders.h"
+
+namespace mozilla {
+namespace image {
+
+class RasterImage;
+
+enum class ICOState
+{
+  HEADER,
+  DIR_ENTRY,
+  SKIP_TO_RESOURCE,
+  FOUND_RESOURCE,
+  SNIFF_RESOURCE,
+  READ_PNG,
+  READ_BIH,
+  READ_BMP,
+  PREPARE_FOR_MASK,
+  READ_MASK_ROW,
+  FINISH_MASK,
+  SKIP_MASK,
+  FINISHED_RESOURCE
+};
+
+class nsICODecoder : public Decoder
+{
+public:
+  virtual ~nsICODecoder() { }
+
+  /// @return the width of the icon directory entry @aEntry.
+  static uint32_t GetRealWidth(const IconDirEntry& aEntry)
+  {
+    return aEntry.mWidth == 0 ? 256 : aEntry.mWidth;
+  }
+
+  /// @return the width of the selected directory entry (mDirEntry).
+  uint32_t GetRealWidth() const { return GetRealWidth(mDirEntry); }
+
+  /// @return the height of the icon directory entry @aEntry.
+  static uint32_t GetRealHeight(const IconDirEntry& aEntry)
+  {
+    return aEntry.mHeight == 0 ? 256 : aEntry.mHeight;
+  }
+
+  /// @return the height of the selected directory entry (mDirEntry).
+  uint32_t GetRealHeight() const { return GetRealHeight(mDirEntry); }
+
+  /// @return the size of the selected directory entry (mDirEntry).
+  gfx::IntSize GetRealSize() const
+  {
+    return gfx::IntSize(GetRealWidth(), GetRealHeight());
+  }
+
+  /// @return The offset from the beginning of the ICO to the first resource.
+  size_t FirstResourceOffset() const;
+
+  LexerResult DoDecode(SourceBufferIterator& aIterator,
+                       IResumable* aOnResume) override;
+  nsresult FinishInternal() override;
+  nsresult FinishWithErrorInternal() override;
+
+private:
+  friend class DecoderFactory;
+
+  // Decoders should only be instantiated via DecoderFactory.
+  explicit nsICODecoder(RasterImage* aImage);
+
+  // Writes to the contained decoder and sets the appropriate errors
+  // Returns true if there are no errors.
+  bool WriteToContainedDecoder(const char* aBuffer, uint32_t aCount);
+
+  // Gets decoder state from the contained decoder so it's visible externally.
+  nsresult GetFinalStateFromContainedDecoder();
+
+  /**
+   * Verifies that the width and height values in @aBIH are valid and match the
+   * values we read from the ICO directory entry. If everything looks OK, the
+   * height value in @aBIH is updated to compensate for the AND mask, which the
+   * underlying BMP decoder doesn't know about.
+   *
+   * @return true if the width and height values in @aBIH are valid and correct.
+   */
+  bool CheckAndFixBitmapSize(int8_t* aBIH);
+
+  // Obtains the number of colors from the BPP, mBPP must be filled in
+  uint16_t GetNumColors();
+
+  LexerTransition<ICOState> ReadHeader(const char* aData);
+  LexerTransition<ICOState> ReadDirEntry(const char* aData);
+  LexerTransition<ICOState> SniffResource(const char* aData);
+  LexerTransition<ICOState> ReadPNG(const char* aData, uint32_t aLen);
+  LexerTransition<ICOState> ReadBIH(const char* aData);
+  LexerTransition<ICOState> ReadBMP(const char* aData, uint32_t aLen);
+  LexerTransition<ICOState> PrepareForMask();
+  LexerTransition<ICOState> ReadMaskRow(const char* aData);
+  LexerTransition<ICOState> FinishMask();
+  LexerTransition<ICOState> FinishResource();
+
+  StreamingLexer<ICOState, 32> mLexer; // The lexer.
+  RefPtr<Decoder> mContainedDecoder; // Either a BMP or PNG decoder.
+  RefPtr<SourceBuffer> mContainedSourceBuffer;  // SourceBuffer for mContainedDecoder.
+  UniquePtr<uint8_t[]> mMaskBuffer;    // A temporary buffer for the alpha mask.
+  char mBIHraw[bmp::InfoHeaderLength::WIN_ICO]; // The bitmap information header.
+  IconDirEntry mDirEntry;              // The dir entry for the selected resource.
+  gfx::IntSize mBiggestResourceSize;   // Used to select the intrinsic size.
+  gfx::IntSize mBiggestResourceHotSpot; // Used to select the intrinsic size.
+  uint16_t mBiggestResourceColorDepth; // Used to select the intrinsic size.
+  int32_t mBestResourceDelta;          // Used to select the best resource.
+  uint16_t mBestResourceColorDepth;    // Used to select the best resource.
+  uint16_t mNumIcons; // Stores the number of icons in the ICO file.
+  uint16_t mCurrIcon; // Stores the current dir entry index we are processing.
+  uint16_t mBPP;      // The BPP of the resource we're decoding.
+  uint32_t mMaskRowSize;  // The size in bytes of each row in the BMP alpha mask.
+  uint32_t mCurrMaskLine; // The line of the BMP alpha mask we're processing.
+  bool mIsCursor;         // Is this ICO a cursor?
+  bool mHasMaskAlpha;     // Did the BMP alpha mask have any transparency?
+};
+
+} // namespace image
+} // namespace mozilla
+
+#endif // mozilla_image_decoders_nsICODecoder_h