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

third_party/WebKit/Source/platform/image-decoders/gif/GIFImageDecoder.cpp

Index: third_party/WebKit/Source/platform/image-decoders/gif/GIFImageDecoder.cpp
diff --git a/third_party/WebKit/Source/platform/image-decoders/gif/GIFImageDecoder.cpp b/third_party/WebKit/Source/platform/image-decoders/gif/GIFImageDecoder.cpp
index a769b6d09bb28180c851a3f3e7128ba6077dbcf1..4bce6ba97fca0811b9e952ec6eafd03677c65e61 100644
--- a/third_party/WebKit/Source/platform/image-decoders/gif/GIFImageDecoder.cpp
+++ b/third_party/WebKit/Source/platform/image-decoders/gif/GIFImageDecoder.cpp
@@ -356,12 +356,17 @@ bool GIFImageDecoder::initFrameBuffer(size_t frameIndex)
         if (!buffer->setSizeAndColorProfile(size().width(), size().height(), ImageFrame::ICCProfile()))
             return setFailed();
     } 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();
+        // We try to reuse |prevBuffer| as starting state and avoid copy.

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

See comments in WebP decoder, they also apply to this file

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

Done.

+        // For DisposeOverwritePrevious, the next frame will also use
+        // |prevBuffer| as its starting state, so we can't take over its image
+        // data using takeBitmapDataIfWritable.  Copy the data instead.
+        if (buffer->getDisposalMethod() == ImageFrame::DisposeOverwritePrevious || !buffer->takeBitmapDataIfWritable(prevBuffer)) {
+            if (!buffer->copyBitmapData(*prevBuffer))
+                return setFailed();
+        }
 
         if (prevBuffer->getDisposalMethod() == ImageFrame::DisposeOverwriteBgcolor) {
             // We want to clear the previous frame to transparent, without