Propagate media play/pause to WebContentsObserver for Chromecast metrics

Propagate OnMedia{Playing,Paused}Notification to WebContentsObserver and use
this to track Chromecast metrics.

BUG=417000

Review URL: https://codereview.chromium.org/1037593003

Cr-Commit-Position: refs/heads/master@{#322282}

chromecast/browser/cast_content_window.cc

@@ -119,4 +119,12 @@ void CastContentWindow::DidFirstVisuallyNonEmptyPaint() {
   metrics::CastMetricsHelper::GetInstance()->LogTimeToFirstPaint();
 }
 
+void CastContentWindow::MediaPaused() {
+  metrics::CastMetricsHelper::GetInstance()->LogMediaPause();
+}
+
+void CastContentWindow::MediaStartedPlaying() {
+  metrics::CastMetricsHelper::GetInstance()->LogMediaPlay();
+}
+
 }  // namespace chromecast

chromecast/browser/cast_content_window.h

@@ -44,6 +44,8 @@ class CastContentWindow : public content::WebContentsObserver {
 
   // content::WebContentsObserver implementation:
   void DidFirstVisuallyNonEmptyPaint() override;
+  void MediaPaused() override;
+  void MediaStartedPlaying() override;
 
  private:
 #if defined(USE_AURA)

content/browser/web_contents/web_contents_impl.cc

@@ -3326,12 +3326,16 @@ void WebContentsImpl::OnMediaPlayingNotification(int64 player_cookie,
     if (!video_power_save_blocker_ && !IsHidden())
       CreateVideoPowerSaveBlocker();
   }
+
+  FOR_EACH_OBSERVER(WebContentsObserver, observers_, MediaStartedPlaying());
 }
 
 void WebContentsImpl::OnMediaPausedNotification(int64 player_cookie) {
   RemoveMediaPlayerEntry(player_cookie, &active_audio_players_);
   RemoveMediaPlayerEntry(player_cookie, &active_video_players_);
   MaybeReleasePowerSaveBlockers();
+
+  FOR_EACH_OBSERVER(WebContentsObserver, observers_, MediaPaused());
 }
 
 void WebContentsImpl::OnFirstVisuallyNonEmptyPaint() {

content/public/browser/web_contents_observer.h

@@ -343,6 +343,12 @@ class CONTENT_EXPORT WebContentsObserver : public IPC::Listener,
   // Invoked when theme color is changed to |theme_color|.
   virtual void DidChangeThemeColor(SkColor theme_color) {}
 
+  // Invoked when media is playing.
+  virtual void MediaStartedPlaying() {}
+
+  // Invoked when media is paused.
+  virtual void MediaPaused() {}
+
   // Invoked if an IPC message is coming from a specific RenderFrameHost.
   virtual bool OnMessageReceived(const IPC::Message& message,
                                  RenderFrameHost* render_frame_host);