Fix race condition:

There is a race condition between AudioRenderer::Reinitialize and

audio_clock_ to null. Sometimes webmediaplayerimpl can request a
timestamp from the pipeline->renderer->audio_renderer which could race
with an ongoing track switch doing a reinitialize.

AudioRenderer: :CurrentMediaTime where reinitialize was setting
Bug: 863764
Change-Id: I6d6a32be37c42bde37d1d02353e3f43a58ab4e66
Reviewed-on: https://chromium-review.googlesource.com/1142899Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Ted Meyer <tmathmeyer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577050}

media/renderers/renderer_impl.cc

@@ -271,6 +271,7 @@ base::TimeDelta RendererImpl::GetMediaTime() {
       return restarting_audio_time_;
     }
   }
+
   return time_source_->CurrentMediaTime();
 }
 
@@ -619,12 +620,12 @@ void RendererImpl::RestartAudioRenderer(
     return;
   }
 
-  audio_renderer_->StartPlaying();
   {
     base::AutoLock lock(restarting_audio_lock_);
     audio_playing_ = true;
     pending_audio_track_change_ = false;
   }
+  audio_renderer_->StartPlaying();
   std::move(restart_completed_cb).Run();
 }
 
@@ -646,9 +647,9 @@ void RendererImpl::RestartVideoRenderer(
     return;
   }
 
-  video_renderer_->StartPlayingFrom(time);
   video_playing_ = true;
   pending_video_track_change_ = false;
+  video_renderer_->StartPlayingFrom(time);
   std::move(restart_completed_cb).Run();
 }
 
@@ -904,15 +905,9 @@ void RendererImpl::OnVideoOpacityChange(bool opaque) {
 }
 
 void RendererImpl::CleanUpTrackChange(base::RepeatingClosure on_finished,
-                                      bool* pending_change,
                                       bool* ended,
                                       bool* playing) {
-  {
-    // This lock is required for setting pending_audio_track_change_, and has
-    // no effect when setting pending_video_track_change_.
-    base::AutoLock lock(restarting_audio_lock_);
-    *pending_change = *ended = *playing = false;
-  }
+  *ended = *playing = false;
   std::move(on_finished).Run();
 }
 
@@ -945,8 +940,7 @@ void RendererImpl::OnSelectedVideoTracksChanged(
   pending_video_track_change_ = true;
   video_renderer_->Flush(base::BindRepeating(
       &RendererImpl::CleanUpTrackChange, weak_this_,
-      base::Passed(&fix_stream_cb), &pending_video_track_change_, &video_ended_,
-      &video_playing_));
+      base::Passed(&fix_stream_cb), &video_ended_, &video_playing_));
 }
 
 void RendererImpl::OnEnabledAudioTracksChanged(
@@ -987,8 +981,7 @@ void RendererImpl::OnEnabledAudioTracksChanged(
 
   audio_renderer_->Flush(base::BindRepeating(
       &RendererImpl::CleanUpTrackChange, weak_this_,
-      base::Passed(&fix_stream_cb), &pending_audio_track_change_, &audio_ended_,
-      &audio_playing_));
+      base::Passed(&fix_stream_cb), &audio_ended_, &audio_playing_));
 }
 
 }  // namespace media

media/renderers/renderer_impl.h

@@ -148,7 +148,6 @@ class MEDIA_EXPORT RendererImpl : public Renderer {
 
   // Fix state booleans after the stream switching is finished.
   void CleanUpTrackChange(base::RepeatingClosure on_finished,
-                          bool* pending_change,
                           bool* ended,
                           bool* playing);