Add UMA stats for starting and stopping video capture.

It
* logs whenever we try to start capture for a client.
* logs the stop reason when we stop capture for a client (normal or due to an error).

Stop capture due to an error can happen when opening the device (async operation), during the session, or when closing down.

BUG=399835

Review URL: https://codereview.chromium.org/464383002

Cr-Commit-Position: refs/heads/master@{#289789}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289789 0039d316-1c4b-4281-b951-d872f2087c98

content/browser/renderer_host/media/video_capture_manager.cc

@@ -75,6 +75,22 @@ void ConsolidateCaptureFormats(media::VideoCaptureFormats* formats) {
 const int kMaxNumberOfBuffers = 3;
 const int kMaxNumberOfBuffersForTabCapture = 5;
 
+// Used for logging capture events.
+// Elements in this enum should not be deleted or rearranged; the only
+// permitted operation is to add new elements before NUM_VIDEO_CAPTURE_EVENT.
+enum VideoCaptureEvent {
+  VIDEO_CAPTURE_EVENT_START_CAPTURE = 0,
+  VIDEO_CAPTURE_EVENT_STOP_CAPTURE_NORMAL = 1,
+  VIDEO_CAPTURE_EVENT_STOP_CAPTURE_DUE_TO_ERROR = 2,
+  NUM_VIDEO_CAPTURE_EVENT
+};
+
+void LogVideoCaptureEvent(VideoCaptureEvent event) {
+  UMA_HISTOGRAM_ENUMERATION("Media.VideoCaptureManager.Event",
+                            event,
+                            NUM_VIDEO_CAPTURE_EVENT);
+}
+
 }  // namespace
 
 namespace content {
@@ -287,6 +303,8 @@ void VideoCaptureManager::StartCaptureForClient(
 
   DCHECK(entry->video_capture_controller);
 
+  LogVideoCaptureEvent(VIDEO_CAPTURE_EVENT_START_CAPTURE);
+
   // First client starts the device.
   if (entry->video_capture_controller->GetClientCount() == 0) {
     DVLOG(1) << "VideoCaptureManager starting device (type = "
@@ -317,6 +335,10 @@ void VideoCaptureManager::StopCaptureForClient(
   DCHECK(controller);
   DCHECK(client_handler);
 
+  LogVideoCaptureEvent(aborted_due_to_error ?
+      VIDEO_CAPTURE_EVENT_STOP_CAPTURE_DUE_TO_ERROR :
+      VIDEO_CAPTURE_EVENT_STOP_CAPTURE_NORMAL);
+
   DeviceEntry* entry = GetDeviceEntryForController(controller);
   if (!entry) {
     NOTREACHED();

tools/metrics/histograms/histograms.xml

@@ -11430,6 +11430,12 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <summary>Measures the time taken for VideoCaptureManager::</summary>
 </histogram>
 
+<histogram name="Media.VideoCaptureManager.Event" enum="VideoCaptureEvent">
+  <owner>grunell@chromium.org</owner>
+  <owner>mcasas@chromium.org</owner>
+  <summary>Counts video capture event, such as start and stop capture.</summary>
+</histogram>
+
 <histogram name="Media.VideoCodec" enum="VideoCodec">
   <owner>scherkus@chromium.org</owner>
   <summary>Video codec used in HTML5 media.</summary>
@@ -50150,6 +50156,12 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="0" label="VAAPI_ERROR"/>
 </enum>
 
+<enum name="VideoCaptureEvent" type="int">
+  <int value="0" label="Starting video capture"/>
+  <int value="1" label="Stopping video capture normally"/>
+  <int value="2" label="Stopping video capture due to error"/>
+</enum>
+
 <enum name="VideoCodec" type="int">
   <int value="0" label="kUnknownVideoCodec"/>
   <int value="1" label="kCodecH264"/>