Move audio focus control from media/ to content/ and make it per WebContents.

media/base/android/media_player_bridge.cc

Index: media/base/android/media_player_bridge.cc
diff --git a/media/base/android/media_player_bridge.cc b/media/base/android/media_player_bridge.cc
index ed8854f1b688774a4f00eecca7f4790d88a368b7..e109e2198a834472a1882eab3c61e97aafd708f8 100644
--- a/media/base/android/media_player_bridge.cc
+++ b/media/base/android/media_player_bridge.cc
@@ -456,6 +456,9 @@ void MediaPlayerBridge::UpdateAllowedOperations() {
 }
 
 void MediaPlayerBridge::StartInternal() {
+  if (!manager()->RequestPlay(player_id()))
+    return;
+
   JNIEnv* env = base::android::AttachCurrentThread();
   Java_MediaPlayerBridge_start(env, j_media_player_bridge_.obj());
   if (!time_update_timer_.IsRunning()) {