[webcrypto] Allow crypto operations to be cancelled by the platform implementation.

Source/modules/crypto/CryptoResultImpl.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 32 matching lines @@
 class ScriptPromiseResolverWithContext;
 ExceptionCode webCryptoErrorToExceptionCode(blink::WebCryptoErrorType);
 
 // Wrapper around a Promise to notify completion of the crypto operation.
 //
 // The thread on which CryptoResultImpl was created on is referred to as the
 // "origin thread".
 //
 //  * At creation time there must be an active ExecutionContext.
 //  * The CryptoResult interface must only be called from the origin thread.
-//  * addref() and deref() can be called from any thread.
+//  * ref(), deref(), cancelled() and cancel() can be called from any thread.
 //  * One of the completeWith***() functions must be called, or the
 //    m_resolver will be leaked until the ExecutionContext is destroyed.
 class CryptoResultImpl FINAL : public CryptoResult {
 public:
     ~CryptoResultImpl();
 
     static PassRefPtr<CryptoResultImpl> create(ScriptState*);
 
     virtual void completeWithError(blink::WebCryptoErrorType, const blink::WebString&) OVERRIDE;
     virtual void completeWithBuffer(const blink::WebArrayBuffer&) OVERRIDE;
     virtual void completeWithJson(const char* utf8Data, unsigned length) OVERRIDE;
     virtual void completeWithBoolean(bool) OVERRIDE;
     virtual void completeWithKey(const blink::WebCryptoKey&) OVERRIDE;
     virtual void completeWithKeyPair(const blink::WebCryptoKey& publicKey, const blink::WebCryptoKey& privateKey) OVERRIDE;
+    virtual bool cancelled() const OVERRIDE;
 
     // It is only valid to call this before completion.
     ScriptPromise promise();
 
 private:
+    class WeakResolver;
     explicit CryptoResultImpl(ScriptState*);
 
+    void cancel();
+
     WeakPtr<ScriptPromiseResolverWithContext> m_resolver;
+    volatile int m_cancelled;
 };
 
 } // namespace WebCore
 
 #endif