Make MediaSession a runtime-enabled feature on Desktop.

content/browser/media/media_web_contents_observer.h

Index: content/browser/media/media_web_contents_observer.h
diff --git a/content/browser/media/media_web_contents_observer.h b/content/browser/media/media_web_contents_observer.h
index d902dc9608d40b80ac856590de24396884c16d09..5dd91cd2f6a4d836f43955218937291a57dd4109 100644
--- a/content/browser/media/media_web_contents_observer.h
+++ b/content/browser/media/media_web_contents_observer.h
@@ -13,10 +13,12 @@
 
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
+#include "content/browser/media/session/media_session_controllers_manager.h"
 #include "content/common/content_export.h"
 #include "content/public/browser/web_contents_observer.h"
 
 namespace content {
+
 class PowerSaveBlocker;
 
 // This class manages all RenderFrame based media related managers at the
@@ -39,6 +41,18 @@ class CONTENT_EXPORT MediaWebContentsObserver : public WebContentsObserver {
   void WasShown() override;
   void WasHidden() override;
 
+#if defined(OS_ANDROID)

[DaleCurtis, 2016/02/17 20:16:54]

Can you keep this on MWCOA? I'd like to avoid reintroducing any #ifdefs to this
class. Perhaps by exposing a protected method that derived classes can use to
access the session map?

[mlamouri (slow - plz ping), 2016/02/23 20:27:55]

Done.

+  // Initiates a synchronous MediaSession request for browser side players.
+  //
+  // TODO(dalecurtis): Delete this method once we're no longer using WMPA and
+  // the BrowserMediaPlayerManagers.  Tracked by http://crbug.com/580626
+  bool RequestPlay(RenderFrameHost* render_frame_host,
+                   int delegate_id,
+                   bool has_audio,
+                   bool is_remote,
+                   base::TimeDelta duration);
+#endif // OS_ANDROID
+
   bool has_audio_power_save_blocker_for_testing() const {
     return !!audio_power_save_blocker_;
   }
@@ -91,6 +105,8 @@ class CONTENT_EXPORT MediaWebContentsObserver : public WebContentsObserver {
   scoped_ptr<PowerSaveBlocker> audio_power_save_blocker_;
   scoped_ptr<PowerSaveBlocker> video_power_save_blocker_;
 
+  MediaSessionControllersManager session_controllers_manager_;
+
   DISALLOW_COPY_AND_ASSIGN(MediaWebContentsObserver);
 };