onCompletion = function() {
    // Ignore it if the component is destroyed before getting a response.
    if (self.isDisposed()) {
      return null;
    }
    self.stopProcessing_();
  }
Executes an API promise based request.
@param {function(...):!goog.Promise} executor The request executor.
@param {!Array} parameters The API request array of parameters.
@param {function(*)} onSuccess The response
    handling success callback.
@param {function(*)} onError The response handling
    error callback.
@return {?goog.Promise} The pending promise.