Reland again "Decode GIF image frames on demand".

Source/core/platform/graphics/ImageSource.cpp

Index: Source/core/platform/graphics/ImageSource.cpp
diff --git a/Source/core/platform/graphics/ImageSource.cpp b/Source/core/platform/graphics/ImageSource.cpp
index e01f10149f38d527e5b5a6c78194fe195b77413d..07f164c7f9ba7f7500a520b572965b11cc40cdc7 100644
--- a/Source/core/platform/graphics/ImageSource.cpp
+++ b/Source/core/platform/graphics/ImageSource.cpp
@@ -45,20 +45,11 @@ ImageSource::ImageSource(ImageSource::AlphaOption alphaOption, ImageSource::Gamm
 
 ImageSource::~ImageSource()
 {
-    clear(true);
 }
 
-void ImageSource::clear(bool destroyAll, size_t clearBeforeFrame, SharedBuffer* data, bool allDataReceived)
+size_t ImageSource::clearCacheExceptFrame(size_t clearExceptFrame)
 {
-    if (!destroyAll) {
-        if (m_decoder)
-            m_decoder->clearFrameBufferCache(clearBeforeFrame);
-        return;
-    }
-
-    m_decoder.clear();
-    if (data)
-        setData(data, allDataReceived);
+    return m_decoder ? m_decoder->clearCacheExceptFrame(clearExceptFrame) : 0;
 }
 
 bool ImageSource::initialized() const