feat(enableDebugTools): return ComponentRef

allows for 
```
bootstrap(App, [
  ...HTTP_PROVIDERS,
  ...ROUTER_PROVIDERS
])
.then(enableDebugTools)
```
without breaking the rule of always returning a value in a promise

modules/@angular/platform-browser/src/browser/tools/tools.ts

@@ -18,6 +18,7 @@ var context = <any>global;
  */
 export function enableDebugTools(ref: ComponentRef<any>): void {
   context.ng = new AngularTools(ref);
+  return ref;
 }
 
 /**