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/web_workers/shared/client_message_broker.ts

@@ -142,6 +142,7 @@ class MessageData {
 
   /**
    * Returns the value from the StringMap if present. Otherwise returns null
+   * @internal
    */
   _getValueIfPresent(data: {[key: string]: any}, key: string) {
     if (StringMapWrapper.contains(data, key)) {