GIF Animations "clear from cache related glitch" fix

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 cc5954edf9de97a6391a4c904dc4826cc341741d..992d16c1f970424e6437e24420754c2741b0fe60 100644
--- a/third_party/WebKit/Source/platform/image-decoders/gif/GIFImageDecoder.cpp
+++ b/third_party/WebKit/Source/platform/image-decoders/gif/GIFImageDecoder.cpp
@@ -227,8 +227,28 @@ size_t GIFImageDecoder::clearCacheExceptFrame(size_t clearExceptFrame)
     // All other frames can be cleared.
     while ((clearExceptFrame < m_frameBufferCache.size()) && (m_frameBufferCache[clearExceptFrame].status() == ImageFrame::FrameEmpty))
         clearExceptFrame = m_frameBufferCache[clearExceptFrame].requiredPreviousFrameIndex();
+    if ((clearExceptFrame >= m_frameBufferCache.size()) || (m_frameBufferCache.size() == 1)
+        || (m_frameBufferCache[clearExceptFrame].disposalMethod() != ImageFrame::DisposeOverwritePrevious))
+        return ImageDecoder::clearCacheExceptFrame(clearExceptFrame);
+    // For case with DisposeOverwritePrevious, enumerate through required to
+    // find the one that is complete.
+    size_t frame2 = m_frameBufferCache[clearExceptFrame].requiredPreviousFrameIndex();
+    while ((frame2 < m_frameBufferCache.size()) && (m_frameBufferCache[frame2].status() == ImageFrame::FrameEmpty))
+        frame2 = m_frameBufferCache[frame2].requiredPreviousFrameIndex();
+    return clearCacheExceptTwoFrames(clearExceptFrame, frame2);
+}
+
 
-    return ImageDecoder::clearCacheExceptFrame(clearExceptFrame);
+size_t GIFImageDecoder::clearCacheExceptTwoFrames(size_t dontClearFrame1, size_t dontClearFrame2)
+{
+    size_t frameBytesCleared = 0;
+    for (size_t i = 0; i < m_frameBufferCache.size(); ++i) {
+        if (m_frameBufferCache[i].status() != ImageFrame::FrameEmpty && i != dontClearFrame1 && i != dontClearFrame2) {
+            frameBytesCleared += frameBytesAtIndex(i);
+            clearFrameBuffer(i);
+        }
+    }
+    return frameBytesCleared;
 }
 
 void GIFImageDecoder::clearFrameBuffer(size_t frameIndex)