callback = function() {
                fn(scope, {$event: event});
              }
@ngdoc directive
@name ngClick

@description
The ngClick directive allows you to specify custom behavior when
an element is clicked.

@element ANY
@priority 0
@param {expression} ngClick {@link guide/expression Expression} to evaluate upon
click. ({@link guide/expression#-event- Event object is available as `$event`})

@example
   <example name="ng-click">
     <file name="index.html">
      <button ng-click="count = count + 1" ng-init="count=0">
        Increment
      </button>
      <span>
        count: {{count}}
      </span>
     </file>
     <file name="protractor.js" type="protractor">
       it('should check ng-click', function() {
         expect(element(by.binding('count')).getText()).toMatch('0');
         element(by.css('button')).click();
         expect(element(by.binding('count')).getText()).toMatch('1');
       });
     </file>
   </example>