Add UMA to check whether requestAudioFocus() is successful.

content/browser/media/android/media_session_uma_helper.cc

Index: content/browser/media/android/media_session_uma_helper.cc
diff --git a/content/browser/media/android/media_session_uma_helper.cc b/content/browser/media/android/media_session_uma_helper.cc
index b1b50cadf5fed45722e90dda1e97848df24c2fba..35e79dd9d5d325357b4c4c7f3b05ec6c27e29cc7 100644
--- a/content/browser/media/android/media_session_uma_helper.cc
+++ b/content/browser/media/android/media_session_uma_helper.cc
@@ -29,6 +29,10 @@ void MediaSessionUmaHelper::RecordSessionSuspended(
       static_cast<HistogramBase::Sample>(MediaSessionSuspendedSource::Count));
 }
 
+void MediaSessionUmaHelper::RecordRequestAudioFocusResult(bool result) const {
+  UMA_HISTOGRAM_BOOLEAN("Media.Session.RequestAudioFocusResult", result);
+}
+
 void MediaSessionUmaHelper::OnSessionActive() {
   current_active_time_ = clock_->Now();
 }