Cheaper thread-safe atomic initialization of static references.

Source/platform/graphics/ImageDecodingStore.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 48 matching lines @@
 //
 // THREAD SAFETY
 //
 // All public methods can be used on any thread.
 
 class PLATFORM_EXPORT ImageDecodingStore {
 public:
     static PassOwnPtr<ImageDecodingStore> create() { return adoptPtr(new ImageDecodingStore); }
     ~ImageDecodingStore();
 
-    static ImageDecodingStore* instance();
+    static ImageDecodingStore& instance();
 
     // Access a cached decoder object. A decoder is indexed by origin (ImageFrameGenerator)
     // and scaled size. Return true if the cached object is found.
     bool lockDecoder(const ImageFrameGenerator*, const SkISize& scaledSize, ImageDecoder**);
     void unlockDecoder(const ImageFrameGenerator*, const ImageDecoder*);
     void insertDecoder(const ImageFrameGenerator*, PassOwnPtr<ImageDecoder>);
     void removeDecoder(const ImageFrameGenerator*, const ImageDecoder*);
 
     // Remove all cache entries indexed by ImageFrameGenerator.
     void removeCacheIndexedByGenerator(const ImageFrameGenerator*);
@@ skipping 131 matching lines @@
     //   m_heapLimitInBytes
     //   m_heapMemoryUsageInBytes
     // This mutex also protects calls to underlying skBitmap's
     // lockPixels()/unlockPixels() as they are not threadsafe.
     Mutex m_mutex;
 };
 
 } // namespace blink
 
 #endif