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

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 145da08becaafff25debdbd4808dcbf1316e1c20..d9ca1f0857a5a0716fdd00c99cd8289b0b3fac71 100644
--- a/content/renderer/media/media_stream_impl.cc
+++ b/content/renderer/media/media_stream_impl.cc
@@ -199,6 +199,9 @@ 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.
+    LogUserMediaRequestWithNoResult(true,

[vrk (LEFT CHROMIUM), 2014/08/05 19:05:40]

In general, boolean parameters are not good practice. This function call is
pretty hard to understand unless you go to the definition of the call -- e.g.
what does "true" mean? See comment in LogUserMediaRequestWithNoResult -- you
should modify the logic so that you can simply say here:
LogUserMediaRequestWithNoResult(USER_MEDIA_REQUEST_CANCELLED)

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

Done.

+                                    request->generated,
+                                    request->HasPendingSources());
     DeleteUserMediaRequestInfo(request);
   }
 }
@@ -273,23 +276,8 @@ void MediaStreamImpl::OnStreamGenerated(
 
   UserMediaRequestInfo* request_info = FindUserMediaRequestInfo(request_id);
   if (!request_info) {
-    // This can happen if the request is canceled or the frame reloads while
-    // MediaStreamDispatcher is processing the request.
-    // Only stop the device if the device is not used in another MediaStream.
-    for (StreamDeviceInfoArray::const_iterator device_it = audio_array.begin();
-         device_it != audio_array.end(); ++device_it) {
-      if (!FindLocalSource(*device_it))
-        media_stream_dispatcher_->StopStreamDevice(*device_it);
-    }
-
-    for (StreamDeviceInfoArray::const_iterator device_it = video_array.begin();
-         device_it != video_array.end(); ++device_it) {
-      if (!FindLocalSource(*device_it))
-        media_stream_dispatcher_->StopStreamDevice(*device_it);
-    }
-
     DVLOG(1) << "Request ID not found";
-    return;
+    return OnStreamGeneratedForCancelledRequest(audio_array, video_array);

[vrk (LEFT CHROMIUM), 2014/08/05 19:05:40]

Why did you make this into its own function? Also shouldn't return the result of
a void function - I'm assuming that was a mistake?

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

This was re factoring when reading the code. Originally i was going to add an
histogram count for this scenario but then found out that those are counted as
Cancelled or NotGenerated already. Anyhow it might be interesting to add a
counter here and on OnStreamGenerationFailedForCancelledRequest, if we want to
investigate those buckets further.


Regarding return value:
 I think that contrary to Java, return void is valid in C++. I think I just
acquired this style once I spent too much time cleaning WebRTC with unused
return values. Since this seems to cause confusion I am switching to the most
common use case.

   }
   request_info->generated = true;
 
@@ -332,6 +320,26 @@ void MediaStreamImpl::OnStreamGenerated(
                  weak_factory_.GetWeakPtr()));
 }
 
+// This can happen if the request is canceled or the frame reloads while
+// MediaStreamDispatcher is processing the request.
+// Only stop the device if the device is not used in another MediaStream.
+void MediaStreamImpl::OnStreamGeneratedForCancelledRequest(
+    const StreamDeviceInfoArray& audio_array,
+    const StreamDeviceInfoArray& video_array) {
+  for (StreamDeviceInfoArray::const_iterator device_it = audio_array.begin();
+       device_it != audio_array.end(); ++device_it) {
+    if (!FindLocalSource(*device_it))
+      media_stream_dispatcher_->StopStreamDevice(*device_it);
+  }
+
+  for (StreamDeviceInfoArray::const_iterator device_it = video_array.begin();
+       device_it != video_array.end(); ++device_it) {
+    if (!FindLocalSource(*device_it))
+      media_stream_dispatcher_->StopStreamDevice(*device_it);
+  }
+}
+

[vrk (LEFT CHROMIUM), 2014/08/05 19:05:40]

nit: extra line

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

Done.

+
 // Callback from MediaStreamDispatcher.
 // The requested stream failed to be generated.
 void MediaStreamImpl::OnStreamGenerationFailed(
@@ -701,6 +709,26 @@ void MediaStreamImpl::DeleteUserMediaRequestInfo(
   NOTREACHED();
 }
 
+void MediaStreamImpl::DeleteAllUserMediaRequests() {
+  UserMediaRequests::iterator request_it = user_media_requests_.begin();
+  while (request_it != user_media_requests_.end()) {
+    DVLOG(1) << "MediaStreamImpl@" << this << "::DeleteAllUserMediaRequests: "
+             << "Cancel user media request " << (*request_it)->request_id;
+    // If the request is not generated, it means that a request
+    // has been sent to the MediaStreamDispatcher to generate a stream
+    // but MediaStreamDispatcher has not yet responded and we need to cancel
+    // the request.
+    if (!(*request_it)->generated) {
+      media_stream_dispatcher_->CancelGenerateStream(
+          (*request_it)->request_id, weak_factory_.GetWeakPtr());
+    }
+    LogUserMediaRequestWithNoResult(false,

[vrk (LEFT CHROMIUM), 2014/08/05 19:05:40]

As stated elsewhere, this call should instead look like 
if (!(*request_it)->generated) {
  DCHECK(!(*request_it)->HasPendingSources());
  LogUserMediaRequestWithNoResult(USER_MEDIA_REQUEST_NOT_GENERATED)
} else {
  DCHECK((*request_it)->HasPendingSources());
  LogUserMediaRequestWithNoResult(USER_MEDIA_REQUEST_PENDING_MEDIA_TRACKS)
}

(You could also do a DCHECK_EQ((*request_it)->HasPendingSources(),
(*request_it)->generated) before the if/else)

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

Done. I liked this suggestion.

+                                    (*request_it)->generated,
+                                    (*request_it)->HasPendingSources());
+    request_it = user_media_requests_.erase(request_it);
+  }
+}
+
 MediaStreamImpl::MediaDevicesRequestInfo*
 MediaStreamImpl::FindMediaDevicesRequestInfo(
     int request_id) {
@@ -748,20 +776,7 @@ void MediaStreamImpl::CancelAndDeleteMediaDevicesRequest(
 
 void MediaStreamImpl::FrameWillClose() {
   // Cancel all outstanding UserMediaRequests.
-  UserMediaRequests::iterator request_it = user_media_requests_.begin();
-  while (request_it != user_media_requests_.end()) {
-    DVLOG(1) << "MediaStreamImpl@" << this << "::FrameWillClose: "
-             << "Cancel user media request " << (*request_it)->request_id;
-    // If the request is not generated, it means that a request
-    // has been sent to the MediaStreamDispatcher to generate a stream
-    // but MediaStreamDispatcher has not yet responded and we need to cancel
-    // the request.
-    if (!(*request_it)->generated) {
-      media_stream_dispatcher_->CancelGenerateStream(
-          (*request_it)->request_id, weak_factory_.GetWeakPtr());
-    }
-    request_it = user_media_requests_.erase(request_it);
-  }
+  DeleteAllUserMediaRequests();

[vrk (LEFT CHROMIUM), 2014/08/05 19:05:40]

Why did you move this into its own function?

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

Re-factoring when reading the code.
I wanted to isolate all the places where user_media_requests_ vector gets
touched into simple methods. Thus allowing to more easily verify that all code
paths were logging MediaRequest with no result.

 
   // Loop through all current local sources and stop the sources.
   LocalStreamSources::iterator sources_it = local_sources_.begin();