Credential Manager: Add platform-exposed Credential objects.

Source/modules/credentialmanager/FederatedCredential.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef FederatedCredential_h
 #define FederatedCredential_h
 
 #include "bindings/core/v8/ScriptWrappable.h"
 #include "bindings/core/v8/SerializedScriptValue.h"
 #include "modules/credentialmanager/Credential.h"
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
 class FederatedCredential FINAL : public Credential {
 public:
     static FederatedCredential* create(const String& id, const String& name, const String& avatarURL, const String& federation);
-    virtual ~FederatedCredential();
 
     // FederatedCredential.idl
-    const String& federation() const { return m_federation; }
+    const String& federation() const;
 
 private:
     FederatedCredential(const String& id, const String& name, const String& avatarURL, const String& federation);
-
-    String m_federation;
 };
 
 } // namespace blink
 
 #endif // FederatedCredential_h