dart2js: Fix hints in code base.

pkg/compiler/lib/src/elements/elements.dart

 // Copyright (c) 2012, 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 elements;
 
 
 import '../constants/expressions.dart';
 import '../tree/tree.dart';
 import '../util/util.dart';
 import '../resolution/resolution.dart';
 
 import '../dart2jslib.dart' show InterfaceType,
                                  DartType,
                                  TypeVariableType,
                                  TypedefType,
                                  DualKind,
                                  MessageKind,
                                  DiagnosticListener,
                                  Script,
                                  FunctionType,
                                  Selector,
                                  SourceSpan,
                                  Constant,
                                  Compiler,
                                  Backend,
                                  isPrivateName;
 
 import '../dart_types.dart';
-import '../helpers/helpers.dart';
 
 import '../scanner/scannerlib.dart' show Token,
                                          isUserDefinableOperator,
                                          isMinusOperator;
 
 import '../ordered_typeset.dart' show OrderedTypeSet;
 
 import 'visitor.dart' show ElementVisitor;
 
 part 'names.dart';
@@ skipping 1603 matching lines @@
   bool get isDeclaredByField;
 
   /// Returns `true` if this member is abstract.
   bool get isAbstract;
 
   /// If abstract, [implementation] points to the overridden concrete member,
   /// if any. Otherwise [implementation] points to the member itself.
   Member get implementation;
 }