feat(core/application_ref): Allow asyncronous app initializers.

closes #5929.

Closes #6063

modules/angular2/src/core/application_ref.ts

@@ -217,25 +217,36 @@ export class PlatformRef_ extends PlatformRef {
 
   application(providers: Array<Type | Provider | any[]>): ApplicationRef {
     var app = this._initApp(createNgZone(), providers);
-    return app;
+    if (PromiseWrapper.isPromise(app)) {
+      throw new BaseException(
+          "Cannot use asyncronous app initializers with application. Use asyncApplication instead.");
+    }
+    return <ApplicationRef>app;
   }
 
   asyncApplication(bindingFn: (zone: NgZone) => Promise<Array<Type | Provider | any[]>>,
                    additionalProviders?: Array<Type | Provider | any[]>): Promise<ApplicationRef> {
     var zone = createNgZone();
     var completer = PromiseWrapper.completer();
-    zone.run(() => {
-      PromiseWrapper.then(bindingFn(zone), (providers: Array<Type | Provider | any[]>) => {
-        if (isPresent(additionalProviders)) {
-          providers = ListWrapper.concat(providers, additionalProviders);
-        }
-        completer.resolve(this._initApp(zone, providers));
+    if (bindingFn === null) {
+      completer.resolve(this._initApp(zone, additionalProviders));
+    } else {
+      zone.run(() => {
+        PromiseWrapper.then(bindingFn(zone), (providers: Array<Type | Provider | any[]>) => {
+          if (isPresent(additionalProviders)) {
+            providers = ListWrapper.concat(providers, additionalProviders);
+          }
+          let promise = this._initApp(zone, providers);
+          completer.resolve(promise);
+        });
       });
-    });
+    }
     return completer.promise;
   }
 
-  private _initApp(zone: NgZone, providers: Array<Type | Provider | any[]>): ApplicationRef {
+  private _initApp(zone: NgZone,
+                   providers: Array<Type | Provider | any[]>): Promise<ApplicationRef>|
+      ApplicationRef {
     var injector: Injector;
     var app: ApplicationRef;
     zone.run(() => {
@@ -259,8 +270,12 @@ export class PlatformRef_ extends PlatformRef {
     });
     app = new ApplicationRef_(this, zone, injector);
     this._applications.push(app);
-    _runAppInitializers(injector);
-    return app;
+    var promise = _runAppInitializers(injector);
+    if (promise !== null) {
+      return PromiseWrapper.then(promise, (_) => app);
+    } else {
+      return app;
+    }
   }
 
   dispose(): void {
@@ -273,9 +288,22 @@ export class PlatformRef_ extends PlatformRef {
   _applicationDisposed(app: ApplicationRef): void { ListWrapper.remove(this._applications, app); }
 }
 
-function _runAppInitializers(injector: Injector): void {
+function _runAppInitializers(injector: Injector): Promise<any> {
   let inits: Function[] = injector.getOptional(APP_INITIALIZER);
-  if (isPresent(inits)) inits.forEach(init => init());
+  let promises: Promise<any>[] = [];
+  if (isPresent(inits)) {
+    inits.forEach(init => {
+      var retVal = init();
+      if (PromiseWrapper.isPromise(retVal)) {
+        promises.push(retVal);
+      }
+    });
+  }
+  if (promises.length > 0) {
+    return PromiseWrapper.all(promises);
+  } else {
+    return null;
+  }
 }
 
 /**