Settings: Restart volumizers explicitly on resume.

onBindView is no longer called in all cases, so use
onResume as an additional signal that the user returned
to the settings page.  onActivityStop is called in both
cases to cleanup.

Bug: 17461564
Change-Id: I73a6775260951d4fd82ca8c3d8eb852f8dcc7452

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

@@ -120,6 +120,12 @@ public class VolumeSeekBarPreference extends SeekBarPreference
         updateSuppressionText();
     }
 
+    public void onActivityResume() {
+        if (mVolumizer != null) {
+            mVolumizer.start();
+        }
+    }
+
     // during initialization, this preference is the SeekBar listener
     @Override
     public void onProgressChanged(SeekBar seekBar, int progress, boolean fromTouch) {