Plumb audio muting state to guest web-contents.

content/browser/web_contents/web_contents_impl.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/web_contents/web_contents_impl.h"
 
 #include <stddef.h>
 
 #include <utility>
 
@@ skipping 1102 matching lines @@
 
   if (mute) {
     if (!audio_muter_)
       audio_muter_.reset(new WebContentsAudioMuter(this));
     audio_muter_->StartMuting();
   } else {
     DCHECK(audio_muter_);
     audio_muter_->StopMuting();
   }
 
+  // If we have guests, they should have the same audio muting state.

[Charlie Reis, 2016/01/06 22:13:51]

If we use WebContentsObserver for this, it's general and we should omit the
comment (in case it gets stale).

On the flip side, if we just need to notify the guest WebContents(es), could we
iterate over inner_web_contents_tree_nodes_?  Or is that only populated in
--use-cross-process-frames-for-guests?

[wjmaclean, 2016/01/06 22:36:09]

I included the comment to explain who the (typical?) users of this notification
might be, but we can omit it. According to lfg@ inner_web_contents_tree_nodes_
is purely a WebView-over-OOPIF (Woo?) concept.

At present guests *are* the only consumers of this event, but that could
presumably change.

+  FOR_EACH_OBSERVER(WebContentsObserver, observers_,
+                    DidUpdateAudioMutingState(mute));
+
   // Notification for UI updates in response to the changed muting state.
   NotifyNavigationStateChanged(INVALIDATE_TYPE_TAB);
 }
 
 bool WebContentsImpl::IsCrashed() const {
   return (crashed_status_ == base::TERMINATION_STATUS_PROCESS_CRASHED ||
           crashed_status_ == base::TERMINATION_STATUS_ABNORMAL_TERMINATION ||
           crashed_status_ == base::TERMINATION_STATUS_PROCESS_WAS_KILLED ||
 #if defined(OS_CHROMEOS)
           crashed_status_ ==
@@ skipping 3588 matching lines @@
     const WebContentsObserver::MediaPlayerId& id) {
   FOR_EACH_OBSERVER(WebContentsObserver, observers_, MediaStartedPlaying(id));
 }
 
 void WebContentsImpl::MediaStoppedPlaying(
     const WebContentsObserver::MediaPlayerId& id) {
   FOR_EACH_OBSERVER(WebContentsObserver, observers_, MediaStoppedPlaying(id));
 }
 
 }  // namespace content