Detect change on the intersection of video and viewport.

media/remoting/remoting_renderer_controller.h

Index: media/remoting/remoting_renderer_controller.h
diff --git a/media/remoting/remoting_renderer_controller.h b/media/remoting/remoting_renderer_controller.h
index 6c7e24eecd5e67884f21f34e57702a1f8549e0d0..6779313845faeeb371aebfc85ce82693edabcb2f 100644
--- a/media/remoting/remoting_renderer_controller.h
+++ b/media/remoting/remoting_renderer_controller.h
@@ -35,6 +35,7 @@ class RemotingRendererController final : public RemotingSourceImpl::Client,
   // MediaObserver implementations.
   void OnEnteredFullscreen() override;
   void OnExitedFullscreen() override;
+  void OnBecameDominantVisibleContent(bool is_dominant) override;
   void OnSetCdm(CdmContext* cdm_context) override;
   void OnMetadataChanged(const PipelineMetadata& metadata) override;
   void OnRemotePlaybackDisabled(bool disabled) override;
@@ -113,6 +114,9 @@ class RemotingRendererController final : public RemotingSourceImpl::Client,
   // https://w3c.github.io/remote-playback
   bool is_remote_playback_disabled_ = true;
 
+  // Indicates whether video is the dominant visible content in the tab.
+  bool is_dominant_content_ = false;
+
   // The callback to switch the media renderer.
   base::Closure switch_renderer_cb_;