Decorator -- AngularJS

References: 
1. http://docs.angularjs.org/api/AUTO.$provide#constant
2. https://groups.google.com/forum/#!searchin/angular/decorator/angular/72ukcZYeWGE/aMwTXCkKw1QJ

剛好在看$provide.decorator在做什麼，然後在AngularJS的官方mail list中有人討論看到範例就記錄下來以防自己忘記（請參考*2）。

If you want to decorate $http:

ng.config(function ($provide) {

  $provide.decorator('$http', function ($http) {

    // decorate $http

    return $http;

  });

});

If you want to "extend it" (create a new service which prototypally inherits from $http):

myApp.factory('myHttp', function ($http) {

  myHttp = function() {}

  myHttp.prototype = new $http();

  // add other methods

  return myHttp

});