Add UMA to check whether requestAudioFocus() is successful.

content/browser/media/android/media_session.cc

Index: content/browser/media/android/media_session.cc
diff --git a/content/browser/media/android/media_session.cc b/content/browser/media/android/media_session.cc
index 969ee2c5936c619f779ad85a6f8a2bd1bd85b76e..a32159679fa0711ca3c059b47a1b5a190683ff87 100644
--- a/content/browser/media/android/media_session.cc
+++ b/content/browser/media/android/media_session.cc
@@ -288,8 +288,10 @@ bool MediaSession::RequestSystemAudioFocus(Type type) {
 
   JNIEnv* env = base::android::AttachCurrentThread();
   DCHECK(env);
-  return Java_MediaSession_requestAudioFocus(env, j_media_session_.obj(),
-                                             type == Type::Transient);
+  bool result = Java_MediaSession_requestAudioFocus(env, j_media_session_.obj(),
+                                                    type == Type::Transient);
+  uma_helper_.RecordRequestAudioFocusResult(result);
+  return result;
 }
 
 void MediaSession::AbandonSystemAudioFocusIfNeeded() {