Let CastMediaBlocker observe MediaSession instead of WebContents

chromecast/browser/cast_media_blocker.h

Index: chromecast/browser/cast_media_blocker.h
diff --git a/chromecast/browser/cast_media_blocker.h b/chromecast/browser/cast_media_blocker.h
index b3350603f7b1fb448130768b7a7eb26cca37b899..727c50344d294d9a605254cacbd4808209090c70 100644
--- a/chromecast/browser/cast_media_blocker.h
+++ b/chromecast/browser/cast_media_blocker.h
@@ -5,26 +5,23 @@
 #ifndef CHROMECAST_BROWSER_CAST_MEDIA_BLOCKER_H_
 #define CHROMECAST_BROWSER_CAST_MEDIA_BLOCKER_H_
 
-#include "base/macros.h"
+#include "base/callback.h"

[derekjchow1, 2016/10/24 18:50:33]

callback & callback_forward seems redundant.

[Zhiqiang Zhang (Slow), 2016/10/28 10:36:52]

They are all removed since we don't use callback anymore.

 #include "base/callback_forward.h"
-#include "content/public/browser/web_contents_observer.h"
-
-namespace content {
-class WebContents;
-}  // namespace content
+#include "base/macros.h"
+#include "content/public/browser/media_session_observer.h"
 
 namespace chromecast {
 namespace shell {
 
 // This class implements a blocking mode for web applications and is used in
 // Chromecast internal code. Media is unblocked by default.
-class CastMediaBlocker : public content::WebContentsObserver {
+class CastMediaBlocker : public content::MediaSessionObserver {

[derekjchow1, 2016/10/24 18:50:33]

We actually inherit from this class internally, and override other
WebContentsObserver methods. For this CL, inherit from both observer interfaces,
and add a TODO (with my name stapled to it) to remove the WebContentsObserver
interface. I'll decouple the interfaces after your change lands.

  public:
-  explicit CastMediaBlocker(content::WebContents* web_contents);
+  explicit CastMediaBlocker(content::MediaSession* media_session);
 
   // Constructor for test. |suspend_cb| and |resume_cb| will be called when
   // Suspend() and Resume() are called.
-  CastMediaBlocker(content::WebContents* web_contents,
+  CastMediaBlocker(content::MediaSession* media_session,
                    const base::Closure& suspend_cb,
                    const base::Closure& resume_cb);