Reland again "Decode GIF image frames on demand".

Source/core/platform/graphics/chromium/DeferredImageDecoder.cpp

Index: Source/core/platform/graphics/chromium/DeferredImageDecoder.cpp
diff --git a/Source/core/platform/graphics/chromium/DeferredImageDecoder.cpp b/Source/core/platform/graphics/chromium/DeferredImageDecoder.cpp
index f69dbe62cb5d397f722b3d7edd4b5814ea5bf402..774640f9472b0aa477547385feeb821089e33345 100644
--- a/Source/core/platform/graphics/chromium/DeferredImageDecoder.cpp
+++ b/Source/core/platform/graphics/chromium/DeferredImageDecoder.cpp
@@ -171,12 +171,11 @@ int DeferredImageDecoder::repetitionCount() const
     return m_actualDecoder ? m_actualDecoder->repetitionCount() : cAnimationNone;
 }
 
-void DeferredImageDecoder::clearFrameBufferCache(size_t clearBeforeFrame)
+size_t DeferredImageDecoder::clearCacheExceptFrame(size_t clearExceptFrame)
 {
     // If image decoding is deferred then frame buffer cache is managed by
     // the compositor and this call is ignored.
-    if (m_actualDecoder)
-        m_actualDecoder->clearFrameBufferCache(clearBeforeFrame);
+    return m_actualDecoder ? m_actualDecoder->clearCacheExceptFrame(clearExceptFrame) : 0;
 }
 
 bool DeferredImageDecoder::frameHasAlphaAtIndex(size_t index) const