[webcrypto] Make WebCryptoAlgorithm "nullable".

public/platform/WebCryptoAlgorithm.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 67 matching lines @@
 class WebCryptoAesGcmParams;
 class WebCryptoRsaOaepParams;
 
 class WebCryptoAlgorithmParams;
 class WebCryptoAlgorithmPrivate;
 
 // The WebCryptoAlgorithm represents a normalized algorithm and its parameters.
 //   * Immutable
 //   * Threadsafe
 //   * Copiable (cheaply)
+//
+// If WebCryptoAlgorithm "isNull()" then it is invalid to call any of the other
+// methods on it (other than destruction, assignment, or isNull()).
 class WebCryptoAlgorithm {
 public:
 #if BLINK_IMPLEMENTATION
     WebCryptoAlgorithm() { }
     WebCryptoAlgorithm(WebCryptoAlgorithmId, PassOwnPtr<WebCryptoAlgorithmParams>);
 #endif
 
+    BLINK_EXPORT static WebCryptoAlgorithm createNull();
     BLINK_EXPORT static WebCryptoAlgorithm adoptParamsAndCreate(WebCryptoAlgorithmId, WebCryptoAlgorithmParams*);
 
     ~WebCryptoAlgorithm() { reset(); }
 
     WebCryptoAlgorithm(const WebCryptoAlgorithm& other) { assign(other); }
     WebCryptoAlgorithm& operator=(const WebCryptoAlgorithm& other)
     {
         assign(other);
         return *this;
     }
 
+    BLINK_EXPORT bool isNull() const;
+
     BLINK_EXPORT WebCryptoAlgorithmId id() const;
 
     BLINK_EXPORT WebCryptoAlgorithmParamsType paramsType() const;
 
     // Retrieves the type-specific parameters. The algorithm contains at most 1
     // type of parameters. Retrieving an invalid parameter will return 0.
     BLINK_EXPORT const WebCryptoAesCbcParams* aesCbcParams() const;
     BLINK_EXPORT const WebCryptoAesKeyGenParams* aesKeyGenParams() const;
     BLINK_EXPORT const WebCryptoHmacParams* hmacParams() const;
     BLINK_EXPORT const WebCryptoHmacKeyParams* hmacKeyParams() const;
     BLINK_EXPORT const WebCryptoRsaSsaParams* rsaSsaParams() const;
     BLINK_EXPORT const WebCryptoRsaKeyGenParams* rsaKeyGenParams() const;
     BLINK_EXPORT const WebCryptoAesGcmParams* aesGcmParams() const;
     BLINK_EXPORT const WebCryptoRsaOaepParams* rsaOaepParams() const;
 
 private:
     BLINK_EXPORT void assign(const WebCryptoAlgorithm& other);
     BLINK_EXPORT void reset();
 
     WebPrivatePtr<WebCryptoAlgorithmPrivate> m_private;
 };
 
 } // namespace WebKit
 
 #endif