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..0c891536fb7df508b8a365dcf83d1b9694cac127 100644
--- a/content/renderer/media/media_stream_impl.cc
+++ b/content/renderer/media/media_stream_impl.cc
@@ -180,6 +180,7 @@ void MediaStreamImpl::requestUserMedia(
       video_device_id.c_str(),
       mandatory_video ? "true":"false"));
 
+  LogUserMediaRequestEvent(USERMEDIAREQUEST_CREATED);
   user_media_requests_.push_back(
       new UserMediaRequestInfo(request_id, user_media_request,
                                enable_automatic_output_device_selection));
@@ -199,6 +200,7 @@ void MediaStreamImpl::cancelUserMediaRequest(
     // We can't abort the stream generation process.
     // Instead, erase the request. Once the stream is generated we will stop the
     // stream if the request does not exist.
+    LogUserMediaRequestEvent(USERMEDIAREQUEST_CANCELLED);
     DeleteUserMediaRequestInfo(request);
   }
 }
@@ -349,6 +351,7 @@ void MediaStreamImpl::OnStreamGenerationFailed(
   }
 
   GetUserMediaRequestFailed(&request_info->request, result);
+  LogUserMediaRequestResult(result);
   DeleteUserMediaRequestInfo(request_info);
 }
 
@@ -503,6 +506,7 @@ void MediaStreamImpl::OnCreateNativeTracksCompleted(
   else
     GetUserMediaRequestFailed(&request->request, result);
 
+  LogUserMediaRequestResult(result);
   DeleteUserMediaRequestInfo(request);
 }
 
@@ -758,6 +762,7 @@ void MediaStreamImpl::FrameWillClose() {
       media_stream_dispatcher_->CancelGenerateStream(
           (*request_it)->request_id, weak_factory_.GetWeakPtr());
     }
+    LogUserMediaRequestEvent(USERMEDIAREQUEST_NO_RESPONSE);

[vrk (LEFT CHROMIUM), 2014/08/04 18:22:17]

There are a few different "no response" events that we want to be able to
distinguish:
- gUM is called, and the user never clicks allow/deny
- gUM is called, user clicks allow, and the success callback never returns
- gUM is called, user clicks deny, and the failure callback never returns

I think this would lump the above scenarios into one category. How hard would it
be to separate out these scenarios? If it's difficult, I'm fine with the current
behavior and we can discuss adding this distinction later.

     request_it = user_media_requests_.erase(request_it);
   }