Reorganize constants/* libraries.

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/constructors.dart';
 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,
@@ skipping 1638 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;
 }