Improve GIF decoding performance

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 434 matching lines @@
     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()));
 }
 
+// The first LZW codes in the image is invalid that try to create a loop in
+// dictionary. Decoding should fail, but not infinitely loop or corrupt memory.

[Peter Kasting, 2013/10/03 17:52:27]

Nit: This first sentence got quite mangled and is now very hard to understand. 
Let me re-suggest:

"The first LZW codes in the image are invalid values that try to create a loop
in the dictionary."

+TEST(GIFImageDecoderTest, badInitialCode)
+{
+    RefPtr<SharedBuffer> testData = readFile("/Source/core/platform/image-decoders/testing/bad-initial-code.gif");
+    ASSERT_TRUE(testData.get());
+
+    OwnPtr<GIFImageDecoder> testDecoder(createDecoder());
+    testDecoder->setData(testData.get(), true);
+    EXPECT_EQ(1u, testDecoder->frameCount());
+    ASSERT_TRUE(testDecoder->frameBufferAtIndex(0));
+    EXPECT_TRUE(testDecoder->failed());
+}
+
+// Image has an invalid LZW code that exceeds dictionary size. Decoding should fail.

[Peter Kasting, 2013/10/03 17:52:27]

Nit: Add missing articles: "The image has an invalid LZW code that exceeds the
dictionary size."

+TEST(GIFImageDecoderTest, badCode)
+{
+    RefPtr<SharedBuffer> testData = readFile("/Source/core/platform/image-decoders/testing/bad-code.gif");
+    ASSERT_TRUE(testData.get());
+
+    OwnPtr<GIFImageDecoder> testDecoder(createDecoder());
+    testDecoder->setData(testData.get(), true);
+    EXPECT_EQ(1u, testDecoder->frameCount());
+    ASSERT_TRUE(testDecoder->frameBufferAtIndex(0));
+    EXPECT_TRUE(testDecoder->failed());
+}
+
 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());
 }