Ignore unsupported disposal methods when decoding GIF

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

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 433 matching lines @@
     EXPECT_EQ(frameCount, decoder->frameCount());
     ImageFrame* lastFrame = decoder->frameBufferAtIndex(frameCount - 1);
     EXPECT_EQ(baselineHashes[frameCount - 1], hashSkBitmap(lastFrame->getSkBitmap()));
     decoder->clearCacheExceptFrame(kNotFound);
 
     // Resume decoding of the first frame.
     ImageFrame* firstFrame = decoder->frameBufferAtIndex(0);
     EXPECT_EQ(ImageFrame::FrameComplete, firstFrame->status());
     EXPECT_EQ(baselineHashes[0], hashSkBitmap(firstFrame->getSkBitmap()));
 }
+
+TEST(GIFImageDecoderTest, invalidDisposalMethod)
+{
+    OwnPtr<GIFImageDecoder> decoder = createDecoder();
+
+    // The image has 2 frames, with disposal method 4 and 5, respectively.
+    RefPtr<SharedBuffer> data = readFile("/Source/web/tests/data/invalid-disposal-method.gif");
+    ASSERT_TRUE(data.get());
+    decoder->setData(data.get(), true);
+
+    EXPECT_EQ(2u, decoder->frameCount());
+    // Disposal method 4 is converted to ImageFrame::DisposeOverwritePrevious.
+    EXPECT_EQ(ImageFrame::DisposeOverwritePrevious, decoder->frameBufferAtIndex(0)->disposalMethod());
+    // Disposal method 5 is ignored.
+    EXPECT_EQ(ImageFrame::DisposeNotSpecified, decoder->frameBufferAtIndex(1)->disposalMethod());
+}