Add animation support for WebP images

Source/core/platform/image-decoders/gif/GIFImageDecoder.cpp

Index: Source/core/platform/image-decoders/gif/GIFImageDecoder.cpp
diff --git a/Source/core/platform/image-decoders/gif/GIFImageDecoder.cpp b/Source/core/platform/image-decoders/gif/GIFImageDecoder.cpp
index 28b2f823d94398f2e8929dd06ea7d570db9134c4..9626d7bba264f182c92f628549515950d1286d47 100644
--- a/Source/core/platform/image-decoders/gif/GIFImageDecoder.cpp
+++ b/Source/core/platform/image-decoders/gif/GIFImageDecoder.cpp
@@ -134,6 +134,7 @@ bool GIFImageDecoder::setFailed()
     return ImageDecoder::setFailed();
 }
 
+// FIXME: Can the intermediate |rowBuffer| be avoided?
 bool GIFImageDecoder::haveDecodedRow(size_t frameIndex, const Vector<unsigned char>& rowBuffer, size_t width, size_t rowNumber, unsigned repeatCount, bool writeTransparentPixels)
 {
     const GIFFrameContext* frameContext = m_reader->frameContext(frameIndex);
@@ -242,6 +243,19 @@ bool GIFImageDecoder::frameComplete(size_t frameIndex)
     return true;
 }
 
+size_t GIFImageDecoder::clearCacheExceptFrame(size_t clearExceptFrame)
+{
+    // We need to preserve frames such that:
+    //  1. We don't clear |clearExceptFrame|;
+    //  2. We don't clear any frame from which a future initFrameBuffer() call
+    //     will copy bitmap data.
+    // All other frames can be cleared.
+    while ((clearExceptFrame < m_frameBufferCache.size()) && (m_frameBufferCache[clearExceptFrame].status() == ImageFrame::FrameEmpty))
+        clearExceptFrame = m_frameBufferCache[clearExceptFrame].requiredPreviousFrameIndex();
+
+    return ImageDecoder::clearCacheExceptFrame(clearExceptFrame);
+}
+
 void GIFImageDecoder::clearFrameBuffer(size_t frameIndex)
 {
     if (m_reader && m_frameBufferCache[frameIndex].status() == ImageFrame::FramePartial) {
@@ -347,12 +361,7 @@ bool GIFImageDecoder::initFrameBuffer(size_t frameIndex)
             // affecting pixels in the image outside of the frame.
             const IntRect& prevRect = prevBuffer->originalFrameRect();
             ASSERT(!prevRect.contains(IntRect(IntPoint(), size())));
-            for (int y = prevRect.y(); y < prevRect.maxY(); ++y) {
-                for (int x = prevRect.x(); x < prevRect.maxX(); ++x)
-                    buffer->setRGBA(x, y, 0, 0, 0, 0);
-            }
-            if ((prevRect.width() > 0) && (prevRect.height() > 0))
-                buffer->setHasAlpha(true);
+            buffer->zeroFillFrameRect(prevRect);
         }
     }