Plumb power experiment signal to the renderer.

This CL plumbs the power experiment state to the media players in the
renderer that they are / are not the only playing player.  This
lets the renderer decide whether to start measuring power usage.

Bug: 1017783
Change-Id: I17e9b453c63482b20bf2b9c4d802ff346f7bd44e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1992686Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Frank Liberato <liberato@chromium.org>
Cr-Commit-Position: refs/heads/master@{#729937}

content/browser/media/media_power_experiment_manager.cc

@@ -40,6 +40,8 @@ void MediaPowerExperimentManager::PlayerStopped(
       current_experiment_player_ && *current_experiment_player_ == player_id) {
     current_experiment_player_.reset();
     current_experiment_cb_ = ExperimentCB();
+    // Note that there will be no incoming player; there's exactly one and we're
+    // removing it.
   }
   players_.erase(player_id);
   CheckExperimentState();

content/browser/media/media_web_contents_observer.cc

@@ -360,6 +360,8 @@ void MediaWebContentsObserver::AddMediaPlayerEntry(
     ActiveMediaPlayerMap* player_map) {
   (*player_map)[id.render_frame_host].insert(id.delegate_id);
   if (power_experiment_manager_) {
+    // Bind the callback to a WeakPtr for the frame, so that we won't try to
+    // notify the frame after it's been destroyed.
     power_experiment_manager_->PlayerStarted(
         id,
         base::BindRepeating(&MediaWebContentsObserver::OnExperimentStateChanged,
@@ -426,7 +428,9 @@ void MediaWebContentsObserver::SuspendAllMediaPlayers() {
 
 void MediaWebContentsObserver::OnExperimentStateChanged(MediaPlayerId id,
                                                         bool is_starting) {
-  // TODO(liberato): Notify the player.
+  id.render_frame_host->Send(
+      new MediaPlayerDelegateMsg_NotifyPowerExperimentState(
+          id.render_frame_host->GetRoutingID(), id.delegate_id, is_starting));
 }
 
 void MediaWebContentsObserver::RemoveAllPlayers(

content/common/media/media_player_delegate_messages.h

@@ -68,6 +68,10 @@ IPC_MESSAGE_ROUTED2(MediaPlayerDelegateMsg_BecamePersistentVideo,
                     int /* delegate_id, distinguishes instances */,
                     double /* is_persistent */)
 
+IPC_MESSAGE_ROUTED2(MediaPlayerDelegateMsg_NotifyPowerExperimentState,
+                    int /* delegate_id, distinguishes instances */,
+                    bool /* is experiment starting (true) or stopping? */)
+
 // ----------------------------------------------------------------------------
 // Messages from the renderer notifying the browser of playback state changes.
 // ----------------------------------------------------------------------------

content/renderer/media/renderer_webmediaplayer_delegate.cc

@@ -237,6 +237,8 @@ bool RendererWebMediaPlayerDelegate::OnMessageReceived(
                         OnMediaDelegateVolumeMultiplierUpdate)
     IPC_MESSAGE_HANDLER(MediaPlayerDelegateMsg_BecamePersistentVideo,
                         OnMediaDelegateBecamePersistentVideo)
+    IPC_MESSAGE_HANDLER(MediaPlayerDelegateMsg_NotifyPowerExperimentState,
+                        OnMediaDelegatePowerExperimentState)
     IPC_MESSAGE_UNHANDLED(return false)
   IPC_END_MESSAGE_MAP()
   return true;
@@ -347,6 +349,14 @@ void RendererWebMediaPlayerDelegate::OnMediaDelegateBecamePersistentVideo(
     observer->OnBecamePersistentVideo(value);
 }
 
+void RendererWebMediaPlayerDelegate::OnMediaDelegatePowerExperimentState(
+    int player_id,
+    bool state) {
+  Observer* observer = id_map_.Lookup(player_id);
+  if (observer)
+    observer->OnPowerExperimentState(state);
+}
+
 void RendererWebMediaPlayerDelegate::ScheduleUpdateTask() {
   if (!pending_update_task_) {
     base::ThreadTaskRunnerHandle::Get()->PostTask(

content/renderer/media/renderer_webmediaplayer_delegate.h

@@ -98,6 +98,7 @@ class CONTENT_EXPORT RendererWebMediaPlayerDelegate
   void OnMediaDelegateSuspendAllMediaPlayers();
   void OnMediaDelegateVolumeMultiplierUpdate(int player_id, double multiplier);
   void OnMediaDelegateBecamePersistentVideo(int player_id, bool value);
+  void OnMediaDelegatePowerExperimentState(int player_id, bool state);
 
   // Schedules UpdateTask() to run soon.
   void ScheduleUpdateTask();

media/blink/webmediaplayer_impl.cc

@@ -2428,6 +2428,11 @@ void WebMediaPlayerImpl::OnBecamePersistentVideo(bool value) {
   MaybeSendOverlayInfoToDecoder();
 }
 
+void WebMediaPlayerImpl::OnPowerExperimentState(bool state) {
+  if (power_status_helper_)
+    power_status_helper_->UpdatePowerExperimentState(state);
+}
+
 void WebMediaPlayerImpl::ScheduleRestart() {
   // TODO(watk): All restart logic should be moved into PipelineController.
   if (pipeline_controller_->IsPipelineRunning() &&

media/blink/webmediaplayer_impl.h

@@ -241,6 +241,7 @@ class MEDIA_BLINK_EXPORT WebMediaPlayerImpl
   void OnSeekBackward(double seconds) override;
   void OnVolumeMultiplierUpdate(double multiplier) override;
   void OnBecamePersistentVideo(bool value) override;
+  void OnPowerExperimentState(bool state) override;
   void RequestRemotePlaybackDisabled(bool disabled) override;
 
 #if defined(OS_ANDROID)

third_party/blink/public/platform/media/webmediaplayer_delegate.h

@@ -74,6 +74,10 @@ class BLINK_PLATFORM_EXPORT WebMediaPlayerDelegate {
     // Called to set as the persistent video. A persistent video should hide its
     // controls and go fullscreen.
     virtual void OnBecamePersistentVideo(bool value) = 0;
+
+    // Notify the player that it is now eligible to start recording power
+    // measurements if |state| is true, else it is no longer eligible.
+    virtual void OnPowerExperimentState(bool state) {}
   };
 
   // Returns true if the host frame is hidden or closed.