Reliably cancel in-progress CryptoResult(Impl) upon shutdown.

public/platform/WebCrypto.h

 /*
  * 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 83 matching lines @@
     BLINK_PLATFORM_EXPORT bool cancelled() const;
 
 #if INSIDE_BLINK
     BLINK_PLATFORM_EXPORT explicit WebCryptoResult(const PassRefPtrWillBeRawPtr<CryptoResult>&);
 #endif
 
 private:
     BLINK_PLATFORM_EXPORT void reset();
     BLINK_PLATFORM_EXPORT void assign(const WebCryptoResult&);
 
-    WebPrivatePtr<CryptoResult> m_impl;
+    WebPrivatePtr<CryptoResult, WebPrivatePtrDestructionCrossThread> m_impl;
 };
 
 class WebCryptoDigestor {
 public:
     virtual ~WebCryptoDigestor() { }
 
     // consume() will return |true| on the successful addition of data to the
     // partially generated digest. It will return |false| when that fails. After
     // a return of |false|, consume() should not be called again (nor should
     // finish() be called).
@@ skipping 151 matching lines @@
     // Returns true on success.
     virtual bool serializeKeyForClone(const WebCryptoKey&, WebVector<unsigned char>&) { return false; }
 
 protected:
     virtual ~WebCrypto() { }
 };
 
 } // namespace blink
 
 #endif // WebCrypto_h