countWatchers.js

(function() {
  var root = angular.element(document.getElementsByTagName('body'));
  var watchers = 0;

  var f = function(element) {
    if (element.data().hasOwnProperty('$scope')) {
      watchers += (element.data().$scope.$$watchers || []).length;
    }

    angular.forEach(element.children(), function(childElement) {
      f(angular.element(childElement));
    });
  };

  f(root);

  return watchers;
})();