Reorganize constants/* libraries.

tests/compiler/dart2js/serialization_test.dart

 // Copyright (c) 2015, 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.serialization_test;
 
 import 'dart:io';
 import 'memory_compiler.dart';
 import 'package:async_helper/async_helper.dart';
+import 'package:compiler/src/constants/constructors.dart';
 import 'package:compiler/src/constants/expressions.dart';
 import 'package:compiler/src/dart_types.dart';
 import 'package:compiler/src/dart2jslib.dart';
 import 'package:compiler/src/elements/elements.dart';
 import 'package:compiler/src/elements/visitor.dart';
 import 'package:compiler/src/ordered_typeset.dart';
 import 'package:compiler/src/serialization/serialization.dart';
 import 'package:compiler/src/serialization/json_serializer.dart';
 import 'package:compiler/src/tree/tree.dart';
 
@@ skipping 1021 matching lines @@
         exp1, exp2, 'expression',
         exp1.expression, exp2.expression);
   }
 
   @override
   visitDeferred(DeferredConstantExpression exp1,
                 DeferredConstantExpression exp2) {
     // TODO: implement visitDeferred
   }
 }