dart2js: Fix hints in code base.

pkg/compiler/lib/src/compile_time_constants.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 dart2js.compile_time_constant_evaluator;
 
 import 'constant_system_dart.dart';
 import 'constants/constant_system.dart';
 import 'constants/expressions.dart';
 import 'constants/values.dart';
 import 'dart_types.dart';
 import 'dart2jslib.dart' show Compiler, CompilerTask, MessageKind, WorldImpact, invariant;
 import 'elements/elements.dart';
 import 'elements/modelx.dart' show FunctionElementX;
-import 'helpers/helpers.dart';
 import 'resolution/resolution.dart';
 import 'resolution/operators.dart';
 import 'tree/tree.dart';
 import 'util/util.dart' show Link;
 import 'universe/universe.dart' show CallStructure;
 
 /// A [ConstantEnvironment] provides access for constants compiled for variable
 /// initializers.
 abstract class ConstantEnvironment {
   /// The [ConstantSystem] used by this environment.
@@ skipping 1305 matching lines @@
           // TODO(johnniwinther): Return a [NonConstantValue] instead.
           new ErroneousConstantExpression(), new NullConstantValue());
 }
 
 // TODO(johnniwinther): Avoid the need for this hack.
 TreeElements _analyzeElementEagerly(Compiler compiler, AstElement element) {
   WorldImpact worldImpact = compiler.analyzeElement(element.declaration);
   compiler.enqueuer.resolution.applyImpact(element.declaration, worldImpact);
   return element.resolvedAst.elements;
 }