Add histogram WebRTC.UserMediaRequest.NoResultState to track user media requests with no result.

content/renderer/media/webrtc_uma_histograms.cc

Index: content/renderer/media/webrtc_uma_histograms.cc
diff --git a/content/renderer/media/webrtc_uma_histograms.cc b/content/renderer/media/webrtc_uma_histograms.cc
index 6dc50a397c8e7f222128d2393f3cc73f7a900254..3e804e1d0b81f52303739782b92c246f2f34ca68 100644
--- a/content/renderer/media/webrtc_uma_histograms.cc
+++ b/content/renderer/media/webrtc_uma_histograms.cc
@@ -8,6 +8,12 @@
 
 namespace content {
 
+void LogUserMediaRequestWithNoResult(MediaStreamRequestState state) {
+  UMA_HISTOGRAM_ENUMERATION("WebRTC.UserMediaRequest.NoResultState",
+                            state,
+                            NUM_MEDIA_STREAM_REQUEST_WITH_NO_RESULT);
+}
+
 void LogUserMediaRequestResult(MediaStreamRequestResult result) {
   UMA_HISTOGRAM_ENUMERATION(
       "WebRTC.UserMediaRequest.Result", result, NUM_MEDIA_REQUEST_RESULTS);