Image decoding: Remove deprecated image caching code

Source/platform/graphics/ImageFrameGenerator.h

 /*
  * Copyright (C) 2012 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 78 matching lines @@
     // For testing. |factory| will overwrite the default ImageDecoder creation logic if |factory->create()| returns non-zero.
     void setImageDecoderFactory(PassOwnPtr<ImageDecoderFactory> factory) { m_imageDecoderFactory = factory; }
 
     // These methods are called while m_decodeMutex is locked.
     SkBitmap tryToResumeDecode(const SkISize& scaledSize, size_t index);
 
     // Use the given decoder to decode. If a decoder is not given then try to create one.
     // |complete| will be true if decoding was complete.
     SkBitmap decode(size_t index, ImageDecoder**, bool* complete);
 
-    // Return the next generation ID of a new image object. This is used
-    // to identify images of the same frame from different stages of
-    // progressive decode.
-    size_t nextGenerationId() { return m_decodeCount++; }
-
     SkISize m_fullSize;
     ThreadSafeDataTransport m_data;
     bool m_isMultiFrame;
     bool m_decodeFailedAndEmpty;
     Vector<bool> m_hasAlpha;
-    size_t m_decodeCount;
+    int m_decodeCount;
     OwnPtr<ExternalMemoryAllocator> m_externalAllocator;
 
     OwnPtr<ImageDecoderFactory> m_imageDecoderFactory;
 
     // Prevents multiple decode operations on the same data.
     Mutex m_decodeMutex;
 
     // Protect concurrent access to m_hasAlpha.
     Mutex m_alphaMutex;
 };
 
 } // namespace blink
 
 #endif