Move gif image decoder to SkCodec

third_party/WebKit/Source/platform/image-decoders/ImageDecoder.h

Index: third_party/WebKit/Source/platform/image-decoders/ImageDecoder.h
diff --git a/third_party/WebKit/Source/platform/image-decoders/ImageDecoder.h b/third_party/WebKit/Source/platform/image-decoders/ImageDecoder.h
index 3131b5ff2cd6f622673c55092b42f406272b9f62..14c4255b1ec0681196bcd79084f3ea4bebacacdf 100644
--- a/third_party/WebKit/Source/platform/image-decoders/ImageDecoder.h
+++ b/third_party/WebKit/Source/platform/image-decoders/ImageDecoder.h
@@ -381,6 +381,8 @@ class PLATFORM_EXPORT ImageDecoder {
   // initFrameBuffer() before setting the status to FramePartial. For WebP,
   // however, the status needs to be FrameComplete since the complete buffer is
   // used to do alpha blending in WEBPImageDecoder::applyPostProcessing().
+  // And gif is also treated differently, since it relies on SkCodec which
+  // requires the complete required previous frame.
   //
   // Before calling this, verify that frame |index| exists by checking that
   // |index| is smaller than |m_frameBufferCache|.size().