Reland r158910 "Improve GIF decoding performance"

Source/core/platform/image-decoders/gif/GIFImageDecoder.h

Index: Source/core/platform/image-decoders/gif/GIFImageDecoder.h
diff --git a/Source/core/platform/image-decoders/gif/GIFImageDecoder.h b/Source/core/platform/image-decoders/gif/GIFImageDecoder.h
index 5c946a2187590ea2e6916ba30110f824ed9e759e..27733fa1bccdea13423aa752d293ff823b1dcf08 100644
--- a/Source/core/platform/image-decoders/gif/GIFImageDecoder.h
+++ b/Source/core/platform/image-decoders/gif/GIFImageDecoder.h
@@ -31,6 +31,8 @@
 
 class GIFImageReader;
 
+typedef Vector<unsigned char> GIFRow;
+
 namespace WebCore {
 
     // This class decodes the GIF image format.
@@ -57,7 +59,7 @@ namespace WebCore {
         virtual bool setFailed() OVERRIDE;
 
         // Callbacks from the GIF reader.
-        bool haveDecodedRow(size_t frameIndex, const Vector<unsigned char>& rowBuffer, size_t width, size_t rowNumber, unsigned repeatCount, bool writeTransparentPixels);
+        bool haveDecodedRow(size_t frameIndex, GIFRow::const_iterator rowBegin, size_t width, size_t rowNumber, unsigned repeatCount, bool writeTransparentPixels);
         bool frameComplete(size_t frameIndex);
 
         // For testing.