Fix the crash due to AudioRendererImpl::audio_clock_ being null

media/renderers/audio_renderer_impl.cc

Index: media/renderers/audio_renderer_impl.cc
diff --git a/media/renderers/audio_renderer_impl.cc b/media/renderers/audio_renderer_impl.cc
index 25f4ef34d83c294bfddd2ee7543e81672291036f..24af1fa904b19af0e5882e24aada5a5694f6daa4 100644
--- a/media/renderers/audio_renderer_impl.cc
+++ b/media/renderers/audio_renderer_impl.cc
@@ -337,13 +337,21 @@ void AudioRendererImpl::Initialize(DemuxerStream* stream,
   DCHECK(stream);
   DCHECK_EQ(stream->type(), DemuxerStream::AUDIO);
   DCHECK(!init_cb.is_null());
+
+  base::AutoLock auto_lock(lock_);
   DCHECK(state_ == kUninitialized || state_ == kFlushed);
   DCHECK(sink_.get());
 
   // If we are re-initializing playback (e.g. switching media tracks), stop the
   // sink first.
   if (state_ == kFlushed) {
-    sink_->Stop();
+    // Release the lock while we are stopping the sink to avoid deadlock if the
+    // sink needs to wait for the current Render to finish.
+    auto* sink = sink_.get();
+    {
+      base::AutoUnlock auto_unlock(lock_);
+      sink->Stop();
+    }
     audio_clock_.reset();

[DaleCurtis, 2017/05/17 00:15:52]

Instead just delete the CHECK below seems like that isn't catching any
crashes....

[servolk, 2017/05/17 00:23:31]

Sure, we can probably do this. But I believe that still need to add a lock in
this method. It used to be called only once before the audio renderer was
started and we could assume nothing in the audio renderer could change while
it's being initialized. But now the Initialize method will be called more than
once (during media track switching) and we need to ensure no other thread is
changing the audio renderer while it's being initialized.

[servolk, 2017/05/17 00:27:12]

Done (removed the explicit audio_clock_.reset() here and the check below, the
clock will be recreated on line 465 below anyway).

   }