[webcrypto] Make WebCryptoKey nullable.

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 75 matching lines @@
     // Starts a one-shot cryptographic operation which can complete either
     // synchronously, or asynchronously.
     //
     // Let the WebCryptoResult be called "result".
     //
     // The result should be set exactly once, from the same thread which
     // initiated the operation.
     //
     //   * WebCryptoAlgorithms parameters are guaranteed to be !isNull(),
     //     unless noted otherwise.
+    //   * WebCryptoKey parameters are guaranteeed to be !isNull().
     //   * const unsigned char* data buffers are not valid after return.
     virtual void encrypt(const WebCryptoAlgorithm&, const WebCryptoKey&, const unsigned char* data, unsigned dataSize, WebCryptoResult result) { result.completeWithError(); }
     virtual void decrypt(const WebCryptoAlgorithm&, const WebCryptoKey&, const unsigned char* data, unsigned dataSize, WebCryptoResult result) { result.completeWithError(); }
     virtual void sign(const WebCryptoAlgorithm&, const WebCryptoKey&, const unsigned char* data, unsigned dataSize, WebCryptoResult result) { result.completeWithError(); }
     virtual void verifySignature(const WebCryptoAlgorithm&, const WebCryptoKey&, const unsigned char* signature, unsigned signatureSize, const unsigned char* data, unsigned dataSize, WebCryptoResult result) { result.completeWithError(); }
     virtual void digest(const WebCryptoAlgorithm&, const unsigned char* data, unsigned dataSize, WebCryptoResult result) { result.completeWithError(); }
     virtual void generateKey(const WebCryptoAlgorithm&, bool extractable, WebCryptoKeyUsageMask, WebCryptoResult result) { result.completeWithError(); }
     // The WebCryptoAlgorithm for importKey may be "isNull()" meaning that it
     // was unspecified by the caller.
     virtual void importKey(WebCryptoKeyFormat, const unsigned char* keyData, unsigned keyDataSize, const WebCryptoAlgorithm&, bool extractable, WebCryptoKeyUsageMask, WebCryptoResult result) { result.completeWithError(); }
     virtual void exportKey(WebCryptoKeyFormat, const WebCryptoKey&, WebCryptoResult result) { result.completeWithError(); }
 
 protected:
     virtual ~WebCrypto() { }
 };
 
 } // namespace WebKit
 
 #endif