Force stop hosted test after timeout.

When hosted tests run into a timeout, the outer test method stops.
However, the hosted test itself may continue running and needs to be
forced-stopped to ensure it does not block any resources needed by
subsequent test methods.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=166208204

testutils/src/main/java/com/google/android/exoplayer2/testutil/HostActivity.java

@@ -137,6 +137,12 @@ public final class HostActivity extends Activity implements SurfaceHolder.Callba
         fail(message);
       }
     } else {
+      runOnUiThread(new Runnable() {
+        @Override
+        public void run() {
+          hostedTest.forceStop();
+        }
+      });
       String message = "Test timed out after " + timeoutMs + " ms.";
       Log.e(TAG, message);
       if (failOnTimeout) {