Add helpers library to dart2js.

tests/compiler/dart2js/analyze_unused_dart2js_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyze_unused_dart2js;
 
 import 'package:async_helper/async_helper.dart';
 
+import '../../../sdk/lib/_internal/compiler/implementation/dart2jslib.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/filenames.dart';
 
 import 'analyze_helper.dart';
 
 // Do not remove WHITE_LIST even if it's empty.  The error message for
 // unused members refers to WHITE_LIST by name.
-const Map<String, List<String>> WHITE_LIST = const {};
+const Map<String, List<String>> WHITE_LIST = const {
+  // TODO(johnniwinther): Explicitly check that we use no helpers, both methods
+  // and classes, are used in production code.*/
+  // Helper methods for debugging should never be called from production code:
+  "implementation/helpers/": const [" is never "],
+};
 
 void main() {
   var uri = currentDirectory.resolve(
       'sdk/lib/_internal/compiler/implementation/use_unused_api.dart');
-  asyncTest(() => analyze([uri], WHITE_LIST, analyzeAll: false));
+  asyncTest(() => analyze([uri], WHITE_LIST,
+      analyzeAll: false, checkResults: checkResults));
 }
+
+bool checkResults(Compiler compiler, CollectingDiagnosticHandler handler) {
+  var helperUri = currentDirectory.resolve(
+      'sdk/lib/_internal/compiler/implementation/helpers/helpers.dart');
+  void checkLive(member) {
+    if (member.isFunction()) {
+      if (compiler.enqueuer.resolution.isLive(member)) {
+        compiler.reportHint(member, MessageKind.GENERIC,
+            {'text': "Helper function in production code '$member'."});
+      }
+    } else if (member.isClass()) {
+      if (member.isResolved) {
+        compiler.reportHint(member, MessageKind.GENERIC,
+            {'text': "Helper class in production code '$member'."});
+      } else {
+        member.forEachLocalMember(checkLive);
+      }
+    } else if (member.isTypedef()) {
+      if (member.isResolved) {
+        compiler.reportHint(member, MessageKind.GENERIC,
+            {'text': "Helper typedef in production code '$member'."});
+      }
+    }
+  }
+  compiler.libraries['$helperUri'].forEachLocalMember(checkLive);
+  return handler.checkResults();
+}