Make MediaSession a runtime-enabled feature on Desktop.

content/browser/web_contents/web_contents_impl.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_BROWSER_WEB_CONTENTS_WEB_CONTENTS_IMPL_H_
 #define CONTENT_BROWSER_WEB_CONTENTS_WEB_CONTENTS_IMPL_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 364 matching lines @@
   void Find(int request_id,
             const base::string16& search_text,
             const blink::WebFindOptions& options) override;
   void StopFinding(StopFindAction action) override;
   void InsertCSS(const std::string& css) override;
   bool WasRecentlyAudible() override;
   void GetManifest(const GetManifestCallback& callback) override;
   void HasManifest(const HasManifestCallback& callback) override;
   void ExitFullscreen(bool will_cause_resize) override;
   void ResumeLoadingCreatedWebContents() override;
-#if defined(OS_ANDROID)
   void OnMediaSessionStateChanged();
   void ResumeMediaSession() override;
   void SuspendMediaSession() override;
   void StopMediaSession() override;
 
+#if defined(OS_ANDROID)
   base::android::ScopedJavaLocalRef<jobject> GetJavaWebContents() override;
   virtual WebContentsAndroid* GetWebContentsAndroid();
 #elif defined(OS_MACOSX)
   void SetAllowOtherViews(bool allow) override;
   bool GetAllowOtherViews() override;
 #endif
 
   // Implementation of PageNavigator.
   WebContents* OpenURL(const OpenURLParams& params) override;
 
@@ skipping 942 matching lines @@
   // Adds/removes a callback called on creation of each new WebContents.
   static void AddCreatedCallbackForTesting(const CreatedCallback& callback);
   static void RemoveCreatedCallbackForTesting(const CreatedCallback& callback);
 
   DISALLOW_COPY_AND_ASSIGN(FriendZone);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_WEB_CONTENTS_WEB_CONTENTS_IMPL_H_