Controller for the Toast interim elements.
@ngInject
function MdToastController($mdToast, $scope) {
    // For compatibility with AngularJS 1.6+, we should always use the $onInit hook in
    // interimElements. The $mdCompiler simulates the $onInit hook for all versions.
    this.$onInit = function() {
      var self = this;

      if (self.highlightAction) {
        $scope.highlightClasses = [
          'md-highlight',
          self.highlightClass
        ];
      }

      $scope.$watch(function() { return activeToastContent; }, function() {
        self.content = activeToastContent;
      });

      this.resolve = function() {
        $mdToast.hide( ACTION_RESOLVE );
      };
    };
  }