title: GCM defaultSenderID
body: <p>Could somebody please help me understand what the gcm_defaultSenderId is in the following code (found in onHandleIntent in RegistrationIntentService.java):</p>
  
  <pre><code>InstanceID instanceID = InstanceID.getInstance(this);
              String token = instanceID.getToken(getString(R.string.gcm_defaultSenderId),
                      GoogleCloudMessaging.INSTANCE_ID_SCOPE, null);
              // [END get_token]
              Log.i(TAG, "GCM Registration Token: " + token);
  </code></pre>
  
  <p>This is from the Google sample app for implementing GCM into your app, and it doesn't even compile in their app! I'm sure it's something specific to each app.  I've already added the GCM API to my application, just don't know what this string is supposed to be! Thanks!</p>