Add animation support for WebP images

Source/core/platform/image-decoders/ImageFrame.cpp

Index: Source/core/platform/image-decoders/ImageFrame.cpp
diff --git a/Source/core/platform/image-decoders/ImageFrame.cpp b/Source/core/platform/image-decoders/ImageFrame.cpp
index c597ccca1ec5ea704358340702488a44a2607f58..a0946e87cbfc1b4c02af09a342876e6c8948d245 100644
--- a/Source/core/platform/image-decoders/ImageFrame.cpp
+++ b/Source/core/platform/image-decoders/ImageFrame.cpp
@@ -152,4 +152,17 @@ void ImageFrame::reportMemoryUsage(MemoryObjectInfo* memoryObjectInfo) const
     info.addMember(m_bitmap, "bitmap");
 }
 
+void ImageFrame::zeroFillFrameRect(const IntRect& rect)
+{
+    if (rect.isEmpty())
+        return;
+
+    // FIXME: Can we make this faster using Skia?
+    for (int y = rect.y(); y < rect.maxY(); ++y) {
+        uint8_t* const dst = reinterpret_cast<uint8_t*>(getAddr(rect.x(), rect.y()));
+        memset(dst, 0, (rect.maxX() - rect.x()) * sizeof(ImageFrame::PixelData));
+    }
+    setHasAlpha(true);
+}
+
 } // namespace WebCore