Add a method to tab_utils.h to find out whether a tab is playing audio.

content/test/webrtc_audio_device_test.cc

Index: content/test/webrtc_audio_device_test.cc
diff --git a/content/test/webrtc_audio_device_test.cc b/content/test/webrtc_audio_device_test.cc
index 72d94e597f26827e025df57508383a7f8450237b..e284230986cb3b20aff121d78783a0e1a9184726 100644
--- a/content/test/webrtc_audio_device_test.cc
+++ b/content/test/webrtc_audio_device_test.cc
@@ -230,7 +230,7 @@ void WebRTCAudioDeviceTest::UninitializeIOThread() {
 void WebRTCAudioDeviceTest::CreateChannel(const char* name) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
   audio_render_host_ = new AudioRendererHost(
-      audio_manager_.get(), media_observer_.get());
+      0, audio_manager_.get(), media_observer_.get());
   audio_render_host_->OnChannelConnected(base::GetCurrentProcId());
 
   audio_input_renderer_host_ = new AudioInputRendererHost(