Ember: actually use Controller registry in controllerFor.

types/ember/index.d.ts

@@ -1819,7 +1819,7 @@ declare module 'ember' {
              * The controller instance must already have been created, either through entering the
              * associated route or using `generateController`.
              */
-            controllerFor(name: string): Controller;
+            controllerFor<K extends keyof ControllerRegistry>(name: K): ControllerRegistry[K];
 
             /**
              * Disconnects a view that has been rendered into an outlet.

types/ember/test/inject.ts

@@ -5,6 +5,8 @@ class AuthService extends Ember.Service {
 }
 
 class ApplicationController extends Ember.Controller {
+    model: {};
+    string: string;
     transitionToLogin() {}
 }
 
@@ -29,6 +31,10 @@ class LoginRoute extends Ember.Route {
             this.get('application').transitionToLogin();
         }
     }
+
+    anyOldMethod() {
+        this.controllerFor('application').set('string', 'must be a string');
+    }
 }
 
 // New module injection style.