Ensure that the gesture animation video is paused properly.

Add the handling to pause the animation video when user navigates away
from the gesture settings.

Test: Manual - play gesture animation videos, then switch to another app
in recents. Verifies from logcat that NuPlayerDriver is not active.
Fix: 32064123

Change-Id: I3d0fb3946e4d0d77a686aa97cfabe667862cac17

src/com/android/settings/gestures/GestureSettings.java

@@ -144,6 +144,14 @@ public class GestureSettings extends SettingsPreferenceFragment implements
         }
     }
 
+    @Override
+    public void onStop() {
+        super.onStop();
+        for (GesturePreference preference : mPreferences) {
+            preference.onViewInvisible();
+        }
+    }
+
     @Override
     public boolean onPreferenceChange(Preference preference, Object newValue) {
         boolean enabled = (boolean) newValue;