Save a bitmap copy when advancing to dependent GIF and WebP animation frames

third_party/WebKit/Source/platform/image-decoders/webp/WEBPImageDecoder.cpp

Index: third_party/WebKit/Source/platform/image-decoders/webp/WEBPImageDecoder.cpp
diff --git a/third_party/WebKit/Source/platform/image-decoders/webp/WEBPImageDecoder.cpp b/third_party/WebKit/Source/platform/image-decoders/webp/WEBPImageDecoder.cpp
index 1e55c716838dfe0a1dfd4ad611bfa2dad053086c..176f482a60bfe5b89528b9ebfe7489b8ac43e1de 100644
--- a/third_party/WebKit/Source/platform/image-decoders/webp/WEBPImageDecoder.cpp
+++ b/third_party/WebKit/Source/platform/image-decoders/webp/WEBPImageDecoder.cpp
@@ -252,12 +252,17 @@ bool WEBPImageDecoder::initFrameBuffer(size_t frameIndex)
             return setFailed();
         m_frameBackgroundHasAlpha = !buffer.originalFrameRect().contains(IntRect(IntPoint(), size()));
     } else {
-        const ImageFrame& prevBuffer = m_frameBufferCache[requiredPreviousFrameIndex];
+        ImageFrame& prevBuffer = m_frameBufferCache[requiredPreviousFrameIndex];
         ASSERT(prevBuffer.getStatus() == ImageFrame::FrameComplete);
 
-        // Preserve the last frame as the starting state for this frame.
-        if (!buffer.copyBitmapData(prevBuffer))
-            return setFailed();
+        // Preserve the last frame as the starting state for this frame. We try
+        // to reuse |prevBuffer| as starting state and avoid copy.

[Peter Kasting, 2016/08/26 19:04:04]

Nit: and avoid copy -> to avoid copying

[aleksandar.stojiljkovic, 2016/08/26 21:53:51]

Done.

+        // For BlendAtopPreviousFrame, both frames are required, so we can't
+        // take over its image data using takeBitmapDataIfWritable.
+        if (buffer.getAlphaBlendSource() == ImageFrame::BlendAtopPreviousFrame || !buffer.takeBitmapDataIfWritable(&prevBuffer)) {
+            if (!buffer.copyBitmapData(prevBuffer))

[Peter Kasting, 2016/08/26 19:04:04]

Nit: I'd just combine these two conditionals

[aleksandar.stojiljkovic, 2016/08/26 21:53:51]

Done.

+                return setFailed();
+        }
 
         if (prevBuffer.getDisposalMethod() == ImageFrame::DisposeOverwriteBgcolor) {
             // We want to clear the previous frame to transparent, without