Tab Audio Capture: Browser-side connect/disconnect functionality.

media/audio/audio_output_controller.cc

Index: media/audio/audio_output_controller.cc
diff --git a/media/audio/audio_output_controller.cc b/media/audio/audio_output_controller.cc
index f21da8fb75f429574aa11819d068c06b2a40adc2..e67afbd2ae7a00e7084a5f2f393bfe85c0e8a6f8 100644
--- a/media/audio/audio_output_controller.cc
+++ b/media/audio/audio_output_controller.cc
@@ -137,10 +137,9 @@ void AudioOutputController::DoCreate() {
     return;
   }
 
-  // Everything started okay, so register for state change callbacks if we have
-  // not already done so.
-  if (state_ != kRecreating)
-    audio_manager_->AddOutputDeviceChangeListener(this);
+  // Everything started okay, so re-register for state change callbacks (the
+  // call to DoStopCloseAndClearStream() above de-registered this instance).
+  audio_manager_->AddOutputDeviceChangeListener(this);
 
   // We have successfully opened the stream. Set the initial volume.
   stream_->SetVolume(volume_);
@@ -304,11 +303,12 @@ int AudioOutputController::OnMoreIOData(AudioBus* source,
   TRACE_EVENT0("audio", "AudioOutputController::OnMoreIOData");
 
   {
-    // Check state and do nothing if we are not playing.
+    // Check state.  When not playing, fill the destination with zeros.
     // We are on the hardware audio thread, so lock is needed.
     base::AutoLock auto_lock(lock_);
     if (state_ != kPlaying) {
-      return 0;
+      dest->Zero();
+      return dest->frames();
     }
   }
 
@@ -361,16 +361,11 @@ void AudioOutputController::DoStopCloseAndClearStream(WaitableEvent* done) {
 void AudioOutputController::OnDeviceChange() {
   DCHECK(message_loop_->BelongsToCurrentThread());
 
-  // We should always have a stream by this point.
-  CHECK(stream_);
-
-  // Preserve the original state and shutdown the stream.
+  // Preserve the original state.
   State original_state = state_;
-  stream_->Stop();
-  stream_->Close();
-  stream_ = NULL;
 
-  // Recreate the stream, exit if we ran into an error.
+  // Recreate the stream (DoCreate() will first shut down an existing stream).
+  // Exit if we ran into an error.
   state_ = kRecreating;
   DoCreate();
   if (!stream_ || state_ == kError)
@@ -392,4 +387,39 @@ void AudioOutputController::OnDeviceChange() {
   }
 }
 
+AudioOutputStream::AudioSourceCallback* AudioOutputController::Divert() {
+  // Assumption: AudioRendererHost is calling this method on the IO
+  // BrowserThread.
+  DCHECK(!message_loop_->BelongsToCurrentThread());
+
+  // Block until stream closure is complete because, otherwise, it's possible
+  // for two entities to be pulling audio data at the same time.  In addition,
+  // a side effect of closing the stream is that this controller will be
+  // de-registered from device change events (from AudioManager) during the
+  // "divert."
+  base::WaitableEvent blocker(true, false);
+  message_loop_->PostTask(
+      FROM_HERE,
+      base::Bind(&AudioOutputController::DoStopCloseAndClearStream, this,
+                 &blocker));
+  blocker.Wait();
+
+  return this;
+}
+
+void AudioOutputController::Revert(
+    AudioOutputStream::AudioSourceCallback* asc) {
+  // Assumption: AudioRendererHost is calling this method on the IO
+  // BrowserThread.
+  DCHECK(!message_loop_->BelongsToCurrentThread());
+
+  DCHECK_EQ(this, asc);
+
+  // The following re-creates the normal audio output stream and places it in
+  // the correct playback state.  It also re-registers this controller for
+  // device change events from AudioManager.
+  message_loop_->PostTask(
+      FROM_HERE, base::Bind(&AudioOutputController::OnDeviceChange, this));
+}
+
 }  // namespace media