Trigger talkback for notification volume change

Triggers talkback to say the content description of the title of
notification volume when notification volume is set to vibrate or silent
mode.

Fixes: 285453719
Fixes: 285455826
Test: manually checked when the ring volume is set to 0% and when the
notification volume is set to 0%. Check the video in the bug link.

Change-Id: I4bd65bdbfa41793fc8e32c295185363ca36cc0d7

src/com/android/settings/notification/VolumeSeekBarPreference.java

@@ -242,6 +242,11 @@ public class VolumeSeekBarPreference extends SeekBarPreference {
         mTitle.setContentDescription(contentDescription);
     }
 
+    protected void setAccessibilityLiveRegion(int mode) {
+        if (mTitle == null) return;
+        mTitle.setAccessibilityLiveRegion(mode);
+    }
+
     public interface Callback {
         void onSampleStarting(SeekBarVolumizer sbv);
         void onStreamValueChanged(int stream, int progress);