feat(core): PlatformRef and ApplicationRef support registration of disposal functions.

These functions will be called whenever the platform or application are being disposed.

modules/angular2/src/mock/mock_application_ref.ts

@@ -0,0 +1,24 @@
+import {ApplicationRef} from 'angular2/src/core/application_ref';
+import {Type} from 'angular2/src/core/facade/lang';
+import {ComponentRef} from 'angular2/src/core/linker/dynamic_component_loader';
+import {Provider, Injector} from 'angular2/src/core/di';
+import {NgZone} from 'angular2/src/core/zone/ng_zone';
+import {Promise} from 'angular2/src/core/facade/async';
+
+export class MockApplicationRef extends ApplicationRef {
+  registerBootstrapListener(listener: (ref: ComponentRef) => void): void {}
+
+  registerDisposeListener(dispose: () => void): void {}
+
+  bootstrap(componentType: Type, bindings?: Array<Type | Provider | any[]>): Promise<ComponentRef> {
+    return null;
+  }
+
+  get injector(): Injector { return null; };
+
+  get zone(): NgZone { return null; };
+
+  dispose(): void {}
+
+  get componentTypes(): Type[] { return null; };
+}