Wrap MediaMetadata in base::Optional in content and chrome

content/browser/media/android/browser_media_session_manager.h

 // Copyright 2015 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 CONTENT_BROWSER_MEDIA_ANDROID_BROWSER_MEDIA_SESSION_MANAGER_H_
 #define CONTENT_BROWSER_MEDIA_ANDROID_BROWSER_MEDIA_SESSION_MANAGER_H_
 
 #include "base/macros.h"
 #include "content/common/content_export.h"
 
+namespace base {
+template <typename T> class Optional;
+}  // namespace base
+
 namespace IPC {
 class Message;
-}
+}  // namespace IPC
 
 namespace content {
 
 class RenderFrameHost;
 struct MediaMetadata;
 
 class CONTENT_EXPORT BrowserMediaSessionManager {
  public:
   explicit BrowserMediaSessionManager(RenderFrameHost* render_frame_host);
 
   // Message handlers.
   virtual void OnActivate(int session_id, int request_id);
   virtual void OnDeactivate(int session_id, int request_id);
-  virtual void OnSetMetadata(int session_id, const MediaMetadata& metadata);
+  virtual void OnSetMetadata(
+      int session_id, const base::Optional<MediaMetadata>& metadata);
 
   int GetRoutingID() const;
 
   bool Send(IPC::Message* msg);
 
  private:
   RenderFrameHost* const render_frame_host_;
 
   DISALLOW_COPY_AND_ASSIGN(BrowserMediaSessionManager);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_MEDIA_ANDROID_BROWSER_MEDIA_SESSION_MANAGER_H_