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diff --git a/image/decoders/nsIconDecoder.h b/image/decoders/nsIconDecoder.h
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+++ b/image/decoders/nsIconDecoder.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_nsIconDecoder_h
+#define mozilla_image_decoders_nsIconDecoder_h
+
+#include "Decoder.h"
+#include "StreamingLexer.h"
+#include "SurfacePipe.h"
+
+namespace mozilla {
+namespace image {
+
+class RasterImage;
+
+////////////////////////////////////////////////////////////////////////////////
+// The icon decoder is a decoder specifically tailored for loading icons
+// from the OS. We've defined our own little format to represent these icons
+// and this decoder takes that format and converts it into 24-bit RGB with
+// alpha channel support. It was modeled a bit off the PPM decoder.
+//
+// The format of the incoming data is as follows:
+//
+// The first two bytes contain the width and the height of the icon.
+// The remaining bytes contain the icon data, 4 bytes per pixel, in
+// ARGB order (platform endianness, A in highest bits, B in lowest
+// bits), row-primary, top-to-bottom, left-to-right, with
+// premultiplied alpha.
+//
+////////////////////////////////////////////////////////////////////////////////
+
+class nsIconDecoder : public Decoder {
+ public:
+  virtual ~nsIconDecoder();
+
+  DecoderType GetType() const override { return DecoderType::ICON; }
+
+  LexerResult DoDecode(SourceBufferIterator& aIterator,
+                       IResumable* aOnResume) override;
+
+ private:
+  friend class DecoderFactory;
+
+  // Decoders should only be instantiated via DecoderFactory.
+  explicit nsIconDecoder(RasterImage* aImage);
+
+  enum class State { HEADER, ROW_OF_PIXELS, FINISH };
+
+  LexerTransition<State> ReadHeader(const char* aData);
+  LexerTransition<State> ReadRowOfPixels(const char* aData, size_t aLength);
+  LexerTransition<State> Finish();
+
+  StreamingLexer<State> mLexer;
+  SurfacePipe mPipe;
+  uint32_t mBytesPerRow;
+};
+
+}  // namespace image
+}  // namespace mozilla
+
+#endif  // mozilla_image_decoders_nsIconDecoder_h