Cheaper thread-safe atomic initialization of static references.

Source/core/dom/DOMArrayBufferDeallocationObserver.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef DOMArrayBufferDeallocationObserver_h
 #define DOMArrayBufferDeallocationObserver_h
 
 #include "wtf/ArrayBufferDeallocationObserver.h"
 
 namespace blink {
 
 class DOMArrayBufferDeallocationObserver final : public WTF::ArrayBufferDeallocationObserver {
 public:
-    static DOMArrayBufferDeallocationObserver* instance();
+    static DOMArrayBufferDeallocationObserver& instance();
 
     virtual void arrayBufferDeallocated(unsigned sizeInBytes) override;
 
 protected:
     virtual void blinkAllocatedMemory(unsigned sizeInBytes) override;
 };
 
 } // namespace blink
 
 #endif // DOMArrayBufferDeallocationObserver_h