Add histogram WebRTC.UserMediaRequest.Events to allow to track getUserMedia failures and hangs.

content/renderer/media/media_stream_impl.cc

Index: content/renderer/media/media_stream_impl.cc
diff --git a/content/renderer/media/media_stream_impl.cc b/content/renderer/media/media_stream_impl.cc
index 887b593b9cf42eb91f91e2783d2b82532dcce765..145da08becaafff25debdbd4808dcbf1316e1c20 100644
--- a/content/renderer/media/media_stream_impl.cc
+++ b/content/renderer/media/media_stream_impl.cc
@@ -601,12 +601,14 @@ void MediaStreamImpl::GetUserMediaRequestSucceeded(
     const blink::WebMediaStream& stream,
     blink::WebUserMediaRequest* request_info) {
   DVLOG(1) << "MediaStreamImpl::GetUserMediaRequestSucceeded";
+  LogUserMediaRequestResult(MEDIA_DEVICE_OK);
   request_info->requestSucceeded(stream);
 }
 
 void MediaStreamImpl::GetUserMediaRequestFailed(
     blink::WebUserMediaRequest* request_info,
     content::MediaStreamRequestResult result) {
+  LogUserMediaRequestResult(result);
   switch (result) {
     case MEDIA_DEVICE_OK:
       NOTREACHED();