fix(lint): enforce that module-private members have @internal.

This is needed to prevent leaking internal APIs to users via our published .d.ts typings.
Fixes #4645

Closes #4989

modules/angular2/src/core/render/dom/events/key_events.ts

@@ -99,6 +99,7 @@ export class KeyEventsPlugin extends EventManagerPlugin {
     };
   }
 
+  /** @internal */
   static _normalizeKey(keyName: string): string {
     // TODO: switch to a StringMap if the mapping grows too much
     switch (keyName) {