Reorganize constants/* libraries.

pkg/compiler/lib/src/serialization/modelz.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.
 
 /// Implementation of the element model used for deserialiation.
 ///
 /// These classes are created by [ElementDeserializer] triggered by the
 /// [Deserializer].
 
 library dart2js.serialization.modelz;
 
 import 'serialization.dart';
 import 'keys.dart';
+import '../constants/constructors.dart';
 import '../constants/expressions.dart';
 import '../dart2jslib.dart'
     show Backend,
          Compiler,
          DiagnosticListener,
          Script,
          SourceSpan;
 import '../dart_types.dart';
 import '../elements/elements.dart';
 import '../elements/modelx.dart' show FunctionSignatureX;
@@ skipping 1416 matching lines @@
 
   @override
   accept(ElementVisitor visitor, arg) {
     return visitor.visitFieldParameterElement(this, arg);
   }
 
   @override
   ElementKind get kind => ElementKind.INITIALIZING_FORMAL;
 
 }