feat($controllerProvider): add a has() method for checking the existence of a controller

Fixes #13951

Closes #14109

Author: Vadorequest

src/ng/controller.js

@@ -27,6 +27,15 @@ function $ControllerProvider() {
   var controllers = {},
       globals = false;
 
+  /**
+   * @ngdoc method
+   * @name $controllerProvider#has
+   * @param {string} name Controller name to check.
+   */
+  this.has = function(name) {
+    return controllers.hasOwnProperty(name);
+  };
+
   /**
    * @ngdoc method
    * @name $controllerProvider#register

test/ng/controllerSpec.js

@@ -78,6 +78,23 @@ describe('$controller', function() {
     });
 
 
+    it('should allow checking the availability of a controller', function() {
+      $controllerProvider.register('FooCtrl', noop);
+      $controllerProvider.register('BarCtrl', ['dep1', 'dep2', noop]);
+      $controllerProvider.register({
+        'BazCtrl': noop,
+        'QuxCtrl': ['dep1', 'dep2', noop]
+      });
+
+      expect($controllerProvider.has('FooCtrl')).toBe(true);
+      expect($controllerProvider.has('BarCtrl')).toBe(true);
+      expect($controllerProvider.has('BazCtrl')).toBe(true);
+      expect($controllerProvider.has('QuxCtrl')).toBe(true);
+
+      expect($controllerProvider.has('UnknownCtrl')).toBe(false);
+    });
+
+
     it('should instantiate a controller defined on window if allowGlobals is set',
       inject(function($window) {
         var scope = {};