Convert LooperExecutorTest in AppRTC Demo into JUnit test

webrtc/examples/androidapp/src/org/appspot/apprtc/util/LooperExecutor.java

 /*
  *  Copyright 2015 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 53 matching lines @@
   }
 
   public synchronized void requestStop() {
     if (!running) {
       return;
     }
     running = false;
     handler.post(new Runnable() {
       @Override
       public void run() {
-        Looper.myLooper().quit();
+        handler.getLooper().quit();
         Log.d(TAG, "Looper thread finished.");
       }
     });
   }
 
   // Checks if current thread is a looper thread.
   public boolean checkOnLooperThread() {
     return (Thread.currentThread().getId() == threadId);
   }
 
@@ skipping 38 matching lines @@
       Log.w(TAG, "Running looper executor without calling requestStart()");
       return;
     }
     if (Thread.currentThread().getId() == threadId) {
       runnable.run();
     } else {
       handler.post(runnable);
     }
   }
 
+  /**
+   * Access to the handler for testing purposes.
+   */
+  Handler getHandler() {
+    return handler;
+  }
 }