Reland again "Decode GIF image frames on demand".

Source/core/platform/image-decoders/ico/ICOImageDecoder.cpp

Index: Source/core/platform/image-decoders/ico/ICOImageDecoder.cpp
diff --git a/Source/core/platform/image-decoders/ico/ICOImageDecoder.cpp b/Source/core/platform/image-decoders/ico/ICOImageDecoder.cpp
index 6cd4379d83008a213a597537704da56e474016bd..a84d46d96c78d1d94fac8f43fd79de1536a8c902 100644
--- a/Source/core/platform/image-decoders/ico/ICOImageDecoder.cpp
+++ b/Source/core/platform/image-decoders/ico/ICOImageDecoder.cpp
@@ -102,8 +102,10 @@ size_t ICOImageDecoder::frameCount()
     decode(0, true);
     if (m_frameBufferCache.isEmpty()) {
         m_frameBufferCache.resize(m_dirEntries.size());
-        for (size_t i = 0; i < m_dirEntries.size(); ++i)
+        for (size_t i = 0; i < m_dirEntries.size(); ++i) {
             m_frameBufferCache[i].setPremultiplyAlpha(m_premultiplyAlpha);
+            m_frameBufferCache[i].setRequiredPreviousFrameIndex(notFound);
+        }
     }
     // CAUTION: We must not resize m_frameBufferCache again after this, as
     // decodeAtIndex() may give a BMPImageReader a pointer to one of the
@@ -235,6 +237,7 @@ bool ICOImageDecoder::decodeAtIndex(size_t index)
     if (m_pngDecoders[index]->isSizeAvailable() && (m_pngDecoders[index]->size() != dirEntry.m_size))
         return setFailed();
     m_frameBufferCache[index] = *m_pngDecoders[index]->frameBufferAtIndex(0);
+    m_frameBufferCache[index].setRequiredPreviousFrameIndex(notFound);

[Peter Kasting, 2013/06/03 18:39:10]

Do you need to call setPremultiplyAlpha here as in frameCount() or is that
handled by the PNG decoder?

[Xianzhu, 2013/06/03 18:44:44]

Yes, we need it. Done.

     return !m_pngDecoders[index]->failed() || setFailed();
 }