Wrap MediaMetadata in base::Optional in content and chrome

content/public/browser/web_contents_observer.h

 // Copyright (c) 2012 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_PUBLIC_BROWSER_WEB_CONTENTS_OBSERVER_H_
 #define CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_OBSERVER_H_
 
 #include <stdint.h>
 
 #include "base/macros.h"
+#include "base/optional.h"

[mlamouri (slow - plz ping), 2016/09/01 17:47:49]

can't you forward declare `const T&`?

[Zhiqiang Zhang (Slow), 2016/09/01 18:19:37]

Sorry, I didn't quite follow here.
Do you mean forward declare base::Optional<> or content::MediaMetadata?

[Zhiqiang Zhang (Slow), 2016/09/02 12:11:41]

Done.

 #include "base/process/kill.h"
 #include "base/process/process_handle.h"
 #include "content/common/content_export.h"
 #include "content/public/browser/navigation_controller.h"
 #include "content/public/common/frame_navigate_params.h"
 #include "content/public/common/media_metadata.h"
 #include "content/public/common/resource_type.h"
 #include "content/public/common/security_style.h"
 #include "ipc/ipc_listener.h"
 #include "ipc/ipc_sender.h"
@@ skipping 441 matching lines @@
   // Invoked when media is playing or paused.  |id| is unique per player and per
   // RenderFrameHost.  There may be multiple players within a RenderFrameHost
   // and subsequently within a WebContents.  MediaStartedPlaying() will always
   // be followed by MediaStoppedPlaying() after player teardown.  Observers must
   // release all stored copies of |id| when MediaStoppedPlaying() is received.
   using MediaPlayerId = std::pair<RenderFrameHost*, int>;
   virtual void MediaStartedPlaying(const MediaPlayerId& id) {}
   virtual void MediaStoppedPlaying(const MediaPlayerId& id) {}
 
   // Invoked when media session has changed its state.
-  virtual void MediaSessionStateChanged(bool is_controllable,
-                                        bool is_suspended,
-                                        const MediaMetadata& metadata) {}
+  virtual void MediaSessionStateChanged(
+      bool is_controllable,
+      bool is_suspended,
+      const base::Optional<MediaMetadata>& metadata) {}
 
   // Invoked when the renderer process changes the page scale factor.
   virtual void OnPageScaleFactorChanged(float page_scale_factor) {}
 
   // Invoked if an IPC message is coming from a specific RenderFrameHost.
   virtual bool OnMessageReceived(const IPC::Message& message,
                                  RenderFrameHost* render_frame_host);
 
   // Notification that |contents| has gained focus.
   virtual void OnWebContentsFocused() {}
@@ skipping 28 matching lines @@
   void ResetWebContents();
 
   WebContentsImpl* web_contents_;
 
   DISALLOW_COPY_AND_ASSIGN(WebContentsObserver);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_OBSERVER_H_