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..aff7a0cb602d5b27f13f7e188668a3a35966e1c2 100644
--- a/content/renderer/media/webrtc_uma_histograms.cc
+++ b/content/renderer/media/webrtc_uma_histograms.cc
@@ -8,6 +8,30 @@
 
 namespace content {
 
+void LogUserMediaRequestWithNoResult(bool request_cancelled,
+                                     bool stream_generated,
+                                     bool pending_sources) {
+  enum {

[Mark P, 2014/08/05 18:50:23]

Please explicitly state that elements in this enum should not be deleted or
rearranged; the only permitted operation is to add new elements to the end.

[vrk (LEFT CHROMIUM), 2014/08/05 19:05:41]

Move this enum to content/public/common/media_stream_request.h and change the
signature of this method to LogUserMediaRequestWithNoResult(enum) and shift the
logic accordingly. A logging method in the WebRTC UMA class should not need to
know about things like "if stream_generated is true, then pending_sources is
true" -- that logic should be kept localized to the stream generation code in
MediaStreamImpl.

[andresp-chromium, 2014/08/06 10:13:56]

Done.

[andresp-chromium, 2014/08/06 10:13:56]

Done. But moved the enum into webrtc_uma_histogram, i think it is a better place
and it can be moved to content/public/common/media_stream_request whenever the
need to use it somewhere else arises.

+    USER_MEDIA_REQUEST_CANCELLED,

[Mark P, 2014/08/05 18:50:23]

Please explicitly use = 0, = 1, etc.

[andresp-chromium, 2014/08/06 10:13:56]

Done.

+    USER_MEDIA_REQUEST_NOT_GENERATED,
+    USER_MEDIA_REQUEST_PENDING_MEDIA_TRACKS,
+    NUM_USER_MEDIA_REQUEST_WITH_NO_RESULT
+  };
+
+  // If a stream has been generated then there must be pending sources otherwise
+  // there would have been a result. Additionally there can't be pending sources
+  // before it gets generated.
+  DCHECK(stream_generated ? pending_sources : !pending_sources);

[vrk (LEFT CHROMIUM), 2014/08/05 19:05:41]

FYI, could have done DCHECK_EQ(stream_generated, pending_sources)

[andresp-chromium, 2014/08/06 10:13:56]

Acknowledged.

+
+  UMA_HISTOGRAM_ENUMERATION(
+      "WebRTC.UserMediaRequest.NoResultState",
+      request_cancelled
+          ? USER_MEDIA_REQUEST_CANCELLED
+          : (!stream_generated ? USER_MEDIA_REQUEST_NOT_GENERATED
+                               : USER_MEDIA_REQUEST_PENDING_MEDIA_TRACKS),
+      NUM_USER_MEDIA_REQUEST_WITH_NO_RESULT);
+}
+
 void LogUserMediaRequestResult(MediaStreamRequestResult result) {
   UMA_HISTOGRAM_ENUMERATION(
       "WebRTC.UserMediaRequest.Result", result, NUM_MEDIA_REQUEST_RESULTS);