callback = function(args) {
    setTimeout(function() {
      asyncCallback(args);
    }, 0);
  }
Tests whether the angular global variable is present on a page. Retries
in case the page is just loading slowly.

Asynchronous.

@param {number} attempts Number of times to retry.
@param {boolean} ng12Hybrid Flag set if app is a hybrid of angular 1 and 2
@param {function({version: ?number, message: ?string})} asyncCallback callback