Kill ActivityView's background thread when it's destroyed

We were leaking background threads for every new ActivityView.

Change-Id: I7ce190843265567984f6cda9c85fef478b0ead38

core/java/android/app/ActivityView.java

@@ -239,6 +239,8 @@ public class ActivityView extends ViewGroup {
         }
 
         mTextureView.setSurfaceTextureListener(null);
+
+        mThread.quit();
     }
 
     private void attachToSurfaceWhenReady() {