[webcrypto] Make WebCryptoKey nullable.

public/platform/WebCryptoKey.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 66 matching lines @@
 // a "WebCryptoKeyHandle*".
 //
 // WebCryptoKey is:
 //   * Copiable (cheaply)
 //   * Threadsafe if the embedder's WebCryptoKeyHandle is also threadsafe.
 //
 // The embedder is responsible for creating all WebCryptoKeys, and therefore can
 // safely assume any details regarding the type of the wrapped
 // WebCryptoKeyHandle*.
 //
+// If WebCryptoKey "isNull()" then it is invalid to call any of the other
+// methods on it (other than destruction, assignment, or isNull()).
+//
 // FIXME: Define the interface to use for structured clone.
 //        Cloning across a process boundary will need serialization,
 //        however cloning for in-process workers could just share the same
 //        (threadsafe) handle.
 class WebCryptoKey {
 public:
     ~WebCryptoKey() { reset(); }
 
     WebCryptoKey(const WebCryptoKey& other) { assign(other); }
     WebCryptoKey& operator=(const WebCryptoKey& other)
     {
         assign(other);
         return *this;
     }
 
     // For an explanation of these parameters see:
     // https://dvcs.w3.org/hg/webcrypto-api/raw-file/tip/spec/Overview.html#key-interface-members
     //
     // Note that the caller is passing ownership of the WebCryptoKeyHandle*.
     BLINK_PLATFORM_EXPORT static WebCryptoKey create(WebCryptoKeyHandle*, WebCryptoKeyType, bool extractable, const WebCryptoAlgorithm&, WebCryptoKeyUsageMask);
 
+    BLINK_PLATFORM_EXPORT static WebCryptoKey createNull();
+
     // Returns the opaque key handle that was set by the embedder.
     //   * Safe to downcast to known type (since embedder creates all the keys)
     //   * Returned pointer's lifetime is bound to |this|
     BLINK_PLATFORM_EXPORT WebCryptoKeyHandle* handle() const;
 
     BLINK_PLATFORM_EXPORT WebCryptoKeyType type() const;
     BLINK_PLATFORM_EXPORT bool extractable() const;
     BLINK_PLATFORM_EXPORT const WebCryptoAlgorithm& algorithm() const;
     BLINK_PLATFORM_EXPORT WebCryptoKeyUsageMask usages() const;
 
+    BLINK_PLATFORM_EXPORT bool isNull() const;
+
 private:
     WebCryptoKey() { }
     BLINK_PLATFORM_EXPORT void assign(const WebCryptoKey& other);
     BLINK_PLATFORM_EXPORT void reset();
 
     WebPrivatePtr<WebCryptoKeyPrivate> m_private;
 };
 
 // Base class for the embedder to define its own opaque key handle. The lifetime
 // of this object is controlled by WebCryptoKey using reference counting.
 class WebCryptoKeyHandle {
 public:
     virtual ~WebCryptoKeyHandle() { }
 };
 
 } // namespace WebKit
 
 #endif