Update AudioRenderer API to fire changes in BufferingState.

media/base/pipeline.cc

Index: media/base/pipeline.cc
diff --git a/media/base/pipeline.cc b/media/base/pipeline.cc
index 9a7488094259402a467d4587d1b5c911c6676985..9a8fc7cea96253c22aa5ba2908829b8dab7441f9 100644
--- a/media/base/pipeline.cc
+++ b/media/base/pipeline.cc
@@ -412,6 +412,10 @@ void Pipeline::StateTransitionTask(PipelineStatus status) {
       PlaybackRateChangedTask(GetPlaybackRate());
       VolumeChangedTask(GetVolume());
 
+      // Handle renderers that immediately signal they have enough data.
+      if (!WaitingForEnoughData())
+        StartPlayback();
+
       // We enter this state from either kInitPrerolling or kSeeking. As of now
       // both those states call Preroll(), which means by time we enter this
       // state we've already buffered enough data. Forcefully update the
@@ -420,11 +424,10 @@ void Pipeline::StateTransitionTask(PipelineStatus status) {
       //
       // TODO(scherkus): Remove after renderers are taught to fire buffering
       // state callbacks http://crbug.com/144683
-      DCHECK(WaitingForEnoughData());
-      if (audio_renderer_)
-        BufferingStateChanged(&audio_buffering_state_, BUFFERING_HAVE_ENOUGH);
-      if (video_renderer_)
+      if (video_renderer_) {
+        DCHECK(WaitingForEnoughData());
         BufferingStateChanged(&video_buffering_state_, BUFFERING_HAVE_ENOUGH);
+      }
       return;
 
     case kStopping:
@@ -451,9 +454,9 @@ void Pipeline::DoInitialPreroll(const PipelineStatusCB& done_cb) {
 
   // Preroll renderers.
   if (audio_renderer_) {
-    bound_fns.Push(base::Bind(
-        &AudioRenderer::Preroll, base::Unretained(audio_renderer_.get()),
-        seek_timestamp));
+    bound_fns.Push(base::Bind(&AudioRenderer::StartPlayingFrom,
+                              base::Unretained(audio_renderer_.get()),
+                              seek_timestamp));
   }
 
   if (video_renderer_) {
@@ -522,9 +525,9 @@ void Pipeline::DoSeek(
 
   // Preroll renderers.
   if (audio_renderer_) {
-    bound_fns.Push(base::Bind(
-        &AudioRenderer::Preroll, base::Unretained(audio_renderer_.get()),
-        seek_timestamp));
+    bound_fns.Push(base::Bind(&AudioRenderer::StartPlayingFrom,
+                              base::Unretained(audio_renderer_.get()),
+                              seek_timestamp));
   }
 
   if (video_renderer_) {
@@ -857,8 +860,9 @@ void Pipeline::InitializeAudioRenderer(const PipelineStatusCB& done_cb) {
       demuxer_->GetStream(DemuxerStream::AUDIO),
       done_cb,
       base::Bind(&Pipeline::OnUpdateStatistics, base::Unretained(this)),
-      base::Bind(&Pipeline::OnAudioUnderflow, base::Unretained(this)),
       base::Bind(&Pipeline::OnAudioTimeUpdate, base::Unretained(this)),
+      base::Bind(&Pipeline::BufferingStateChanged, base::Unretained(this),
+                 &audio_buffering_state_),
       base::Bind(&Pipeline::OnAudioRendererEnded, base::Unretained(this)),
       base::Bind(&Pipeline::SetError, base::Unretained(this)));
 }
@@ -879,20 +883,6 @@ void Pipeline::InitializeVideoRenderer(const PipelineStatusCB& done_cb) {
       base::Bind(&Pipeline::GetMediaDuration, base::Unretained(this)));
 }
 
-void Pipeline::OnAudioUnderflow() {
-  if (!task_runner_->BelongsToCurrentThread()) {
-    task_runner_->PostTask(FROM_HERE, base::Bind(
-        &Pipeline::OnAudioUnderflow, base::Unretained(this)));
-    return;
-  }
-
-  if (state_ != kPlaying)
-    return;
-
-  if (audio_renderer_)
-    audio_renderer_->ResumeAfterUnderflow();
-}
-
 void Pipeline::BufferingStateChanged(BufferingState* buffering_state,
                                      BufferingState new_buffering_state) {
   DVLOG(1) << __FUNCTION__ << "(" << *buffering_state << ", "
@@ -904,7 +894,7 @@ void Pipeline::BufferingStateChanged(BufferingState* buffering_state,
 
   // Renderer underflowed.
   if (!was_waiting_for_enough_data && WaitingForEnoughData()) {
-    StartWaitingForEnoughData();
+    PausePlayback();
     return;
   }
 
@@ -926,10 +916,11 @@ bool Pipeline::WaitingForEnoughData() const {
   return false;
 }
 
-void Pipeline::StartWaitingForEnoughData() {
+void Pipeline::PausePlayback() {
   DVLOG(1) << __FUNCTION__;
   DCHECK_EQ(state_, kPlaying);
   DCHECK(WaitingForEnoughData());
+  DCHECK(task_runner_->BelongsToCurrentThread());
 
   if (audio_renderer_)
     audio_renderer_->StopRendering();
@@ -942,6 +933,7 @@ void Pipeline::StartPlayback() {
   DVLOG(1) << __FUNCTION__;
   DCHECK_EQ(state_, kPlaying);
   DCHECK(!WaitingForEnoughData());
+  DCHECK(task_runner_->BelongsToCurrentThread());
 
   if (audio_renderer_) {
     // We use audio stream to update the clock. So if there is such a