Fix teardown of stale AudioStreamMonitor poll callbacks.

content/browser/web_contents/web_contents_impl.cc

Index: content/browser/web_contents/web_contents_impl.cc
diff --git a/content/browser/web_contents/web_contents_impl.cc b/content/browser/web_contents/web_contents_impl.cc
index 9e954d813c5dec1a290def689ce1f51c1f983c6a..9ea129332252f9a3a12efc5e045b68829d5cd4b8 100644
--- a/content/browser/web_contents/web_contents_impl.cc
+++ b/content/browser/web_contents/web_contents_impl.cc
@@ -4398,6 +4398,7 @@ void WebContentsImpl::RenderViewTerminated(RenderViewHost* rvh,
 
   for (auto& observer : observers_)
     observer.RenderProcessGone(GetCrashedStatus());
+  audio_stream_monitor_.RenderProcessGone(rvh->GetProcess()->GetID());

[Max Morin, 2017/02/17 16:39:53]

Actually, this code confuses me. Shouldn't audio_stream_monitor_ be a
RenderProcessHostObserver instead?

[DaleCurtis, 2017/02/17 17:23:03]

Could be, but since WC is the only owner of this class it seemed clearer to have
a single method versus inheriting everything from RPO. Defer to content/ folk on
preference though.

[Charlie Reis, 2017/02/17 21:27:55]

Yeah, I can see both sides, but I see the argument for handling it here.  I'll
suggest moving it up near the other special cases above, like below the
HideValidationMessage call.

[DaleCurtis, 2017/02/17 22:03:59]

Done.

 }
 
 void WebContentsImpl::RenderViewDeleted(RenderViewHost* rvh) {