Make tab audible and muted states and cause available for an extension API

content/browser/media/capture/web_contents_audio_input_stream.cc

Index: content/browser/media/capture/web_contents_audio_input_stream.cc
diff --git a/content/browser/media/capture/web_contents_audio_input_stream.cc b/content/browser/media/capture/web_contents_audio_input_stream.cc
index 605124dd30848e20e6223c7f143baaa9e8003a0e..986307808485a2ca51fa0678b9b8cd229739e1c8 100644
--- a/content/browser/media/capture/web_contents_audio_input_stream.cc
+++ b/content/browser/media/capture/web_contents_audio_input_stream.cc
@@ -23,6 +23,10 @@
 
 namespace content {
 
+// String to indicate that muted state change was caused by capture
+// (instead of initial, user or an extension id).
+static const char kMutedToggleCauseCapture[] = "auto-forced for capture";
+
 class WebContentsAudioInputStream::Impl
     : public base::RefCountedThreadSafe<WebContentsAudioInputStream::Impl>,
       public AudioMirroringManager::MirroringDestination {
@@ -251,7 +255,7 @@ void WebContentsAudioInputStream::Impl::UnmuteWebContentsAudio() {
 
   WebContents* const contents = tracker_->web_contents();
   if (contents)
-    contents->SetAudioMuted(false);
+    contents->SetAudioMuted(false, kMutedToggleCauseCapture);
 }
 
 void WebContentsAudioInputStream::Impl::QueryForMatches(