[webcrypto] Match the error handling defined by the spec.

Source/core/platform/CryptoResult.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 24 matching lines @@
 #include "wtf/RefCounted.h"
 
 namespace WebCore {
 
 // Receives notification of completion of the crypto operation.
 class CryptoResult : public RefCounted<CryptoResult> {
 public:
     virtual ~CryptoResult() { }
 
     virtual void completeWithError() = 0;
+    virtual void completeWithError(const blink::WebString&) = 0;
     virtual void completeWithBuffer(const blink::WebArrayBuffer&) = 0;
     virtual void completeWithBoolean(bool) = 0;
     virtual void completeWithKey(const blink::WebCryptoKey&) = 0;
     virtual void completeWithKeyPair(const blink::WebCryptoKey& publicKey, const blink::WebCryptoKey& privateKey) = 0;
 
     blink::WebCryptoResult result()
     {
         return blink::WebCryptoResult(this);
     }
 };
 
 } // namespace WebCore
 
 #endif