Set audio format before adding pepper sink to audio track.

content/renderer/pepper/pepper_media_stream_audio_track_host.cc

Index: content/renderer/pepper/pepper_media_stream_audio_track_host.cc
diff --git a/content/renderer/pepper/pepper_media_stream_audio_track_host.cc b/content/renderer/pepper/pepper_media_stream_audio_track_host.cc
index c2dacf535cac5df0f916c027e1e66db3458edd59..c8f9e7d51509be2690f9c76caf8558cb2e8a1bd5 100644
--- a/content/renderer/pepper/pepper_media_stream_audio_track_host.cc
+++ b/content/renderer/pepper/pepper_media_stream_audio_track_host.cc
@@ -364,6 +364,13 @@ void PepperMediaStreamAudioTrackHost::OnNewBufferEnqueued() {
 
 void PepperMediaStreamAudioTrackHost::DidConnectPendingHostToResource() {
   if (!connected_) {
+    media::AudioParameters format =
+        MediaStreamAudioSink::GetFormatFromAudioTrack(track_);
+    // Although this should only be called on the audio capture thread, that
+    // can't happen until the sink is added to the audio track below.

[dmichael (off chromium), 2015/01/20 17:07:03]

This seems kind of dangerous. Is there any way for you to get a TaskRunner for
the audio capture thread to post it there?

At the very least, there ought to be an obvious comment on
AudioSink::OnSetFormat to indicate that it must be callable from the main thread
OR the audio capture thread. It looks like it's probably safe for now, but who
knows what a future coder might do...

[DaleCurtis, 2015/01/20 18:46:56]

Yeah the API contract should document this. I'm not sure how the pepper sink
works, so there may also be a task runner you can use. There isn't one for
normal input capture though.

[Anand Mistry (off Chromium), 2015/01/27 02:12:10]

Nope. The audio capture thread is a real-time thread that blocks on a socket. No
TaskRunner available. That's this issue this CL works around.
I've extended the comment in the header file to try and make this clear.

+    if (format.IsValid())
+      audio_sink_.OnSetFormat(format);
+
     MediaStreamAudioSink::AddToAudioTrack(&audio_sink_, track_);
     connected_ = true;
   }