Reland again "Decode GIF image frames on demand".

Source/core/platform/image-decoders/skia/ImageDecoderSkia.cpp

 /*
  * Copyright (C) 2006 Apple Computer, Inc.  All rights reserved.
  * Copyright (C) 2008, 2009 Google, Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 22 matching lines @@
 namespace WebCore {
 
 ImageFrame::ImageFrame()
     : m_bitmap(NativeImageSkia::create())
     , m_allocator(0)
     , m_hasAlpha(false)
     , m_status(FrameEmpty)
     , m_duration(0)
     , m_disposalMethod(DisposeNotSpecified)
     , m_premultiplyAlpha(true)
+    , m_requiredPreviousFrameIndex(notFound)
+#if !ASSERT_DISABLED
+    , m_requiredPreviousFrameIndexValid(false)
+#endif
 {
 }
 
 ImageFrame& ImageFrame::operator=(const ImageFrame& other)
 {
     if (this == &other)
         return *this;
 
     m_bitmap = other.m_bitmap->clone();
     // Keep the pixels locked since we will be writing directly into the
     // bitmap throughout this object's lifetime.
     m_bitmap->bitmap().lockPixels();
     setMemoryAllocator(other.allocator());
     setOriginalFrameRect(other.originalFrameRect());
     setStatus(other.status());
     setDuration(other.duration());
     setDisposalMethod(other.disposalMethod());
     setPremultiplyAlpha(other.premultiplyAlpha());
     // Be sure that this is called after we've called setStatus(), since we
     // look at our status to know what to do with the alpha value.
     setHasAlpha(other.hasAlpha());
+    // Copy raw fields to avoid ASSERT failure in requiredPreviousFrameIndex().
+    m_requiredPreviousFrameIndex = other.m_requiredPreviousFrameIndex;
+#if !ASSERT_DISABLED
+    m_requiredPreviousFrameIndexValid = other.m_requiredPreviousFrameIndexValid;
+#endif
     return *this;
 }
 
 void ImageFrame::clearPixelData()
 {
     m_bitmap->bitmap().reset();
     m_status = FrameEmpty;
     // NOTE: Do not reset other members here; clearFrameBufferCache()
     // calls this to free the bitmap data, but other functions like
     // initFrameBuffer() and frameComplete() may still need to read
@@ skipping 62 matching lines @@
     }
 }
 
 void ImageFrame::reportMemoryUsage(MemoryObjectInfo* memoryObjectInfo) const
 {
     MemoryClassInfo info(memoryObjectInfo, this, PlatformMemoryTypes::Image);
     info.addMember(m_bitmap, "bitmap");
 }
 
 } // namespace WebCore