Migrate ringtone playback to SystemUI.

Introduce IRingtonePlayer, which handles playback for both Ringtone
objects and Notifications. SystemUI now hosts this player, which it
registers with AudioService. It also keeps MediaPlayer instances
warm, and cleans them up after stop() or Binder death.

Move both Ringtone and NotificationManagerService to play back audio
through this new interface.

Bug: 6376128, 6350773
Change-Id: I1dcb86d16ee3c4f07cdb2248d33dcff4ead3609a
diff --git a/core/java/android/app/Notification.java b/core/java/android/app/Notification.java
index 0a996df..69689c9 100644
--- a/core/java/android/app/Notification.java
+++ b/core/java/android/app/Notification.java
@@ -21,6 +21,7 @@
 import android.content.Context;
 import android.content.Intent;
 import android.graphics.Bitmap;
+import android.media.AudioManager;
 import android.net.Uri;
 import android.os.Bundle;
 import android.os.IBinder;
@@ -213,7 +214,7 @@
     /**
      * Use this constant as the value for audioStreamType to request that
      * the default stream type for notifications be used.  Currently the
-     * default stream type is STREAM_RING.
+     * default stream type is {@link AudioManager#STREAM_NOTIFICATION}.
      */
     public static final int STREAM_DEFAULT = -1;