Reland "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..6615c9e89a8ea78455eb011ef2ae89d38dbde7f0 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