Handle getDisplayMedia case in MediaStreamCaptureIndicator

This CL adds getDisplayMedia() calls going through MediaStreamCaptureIndicator
into the existing |desktop_stream_count_|.

Bug: 326740
Change-Id: I4c16e41c281d96bd9012b4bb66381d5c81d351ca
Reviewed-on: https://chromium-review.googlesource.com/1180097Reviewed-by: Weiyong Yao <braveyao@chromium.org>
Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
Commit-Queue: Emircan Uysaler <emircan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584228}

chrome/browser/media/webrtc/media_stream_capture_indicator.cc

@@ -235,9 +235,11 @@ int& MediaStreamCaptureIndicator::WebContentsDeviceUsage::GetStreamCount(
 
     case content::MEDIA_GUM_DESKTOP_VIDEO_CAPTURE:
     case content::MEDIA_GUM_DESKTOP_AUDIO_CAPTURE:
+    case content::MEDIA_DISPLAY_VIDEO_CAPTURE:
       return desktop_stream_count_;
 
-    default:
+    case content::MEDIA_NO_SERVICE:
+    case content::NUM_MEDIA_TYPES:
       NOTREACHED();
       return video_stream_count_;
   }