This allows TypeScript to produce an API surface which matches the Dart semantics.
I found these with:
gulp build.js.dev && find dist/js/dev/es5/angular2/src -name "*.d.ts" -exec grep -H -n '^ *_' {} \;
Closes#4638
Provide the ability to attach custom data onto a route and retrieve
that data as an injectable (RouteData) inside the component.
Closes#2777Closes#3541
