Reorganize constants/* libraries.

pkg/compiler/lib/src/use_unused_api.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.
 
 /// This file use methods that aren't used by dart2js.dart, but that we wish to
 /// keep anyway. This might be general API that isn't currently in use,
 /// debugging aids, or API only used for testing (see TODO below).
 
 library dart2js.use_unused_api;
 
 import '../compiler.dart' as api;
 
 import 'colors.dart' as colors;
 import 'constants/constant_system.dart' as constants;
+import 'constants/constructors.dart' as constants;
+import 'constants/evaluation.dart' as constants;
 import 'constants/expressions.dart' as constants;
 import 'constants/values.dart' as constants;
 import 'cps_ir/cps_ir_builder.dart' as ir_builder;
 import 'cps_ir/cps_ir_builder_task.dart' as ir_builder;
 import 'tree_ir/tree_ir_nodes.dart' as tree_ir;
 import 'dart_types.dart' as dart_types;
 import 'dart2js.dart' as dart2js;
 import 'dart2jslib.dart' as dart2jslib;
 import 'elements/elements.dart' as elements;
 import 'elements/modelx.dart' as modelx;
@@ skipping 51 matching lines @@
   useCodeEmitterTask(null);
   useScript(null);
   useProgramBuilder(null);
   useSemanticVisitor();
   useTreeVisitors();
 }
 
 useApi(api.ReadStringFromUri uri) {
 }
 
-class NullConstantConstructorVisitor extends constants.ConstantConstructorVisitor {
+class NullConstantConstructorVisitor
+    extends constants.ConstantConstructorVisitor {
   @override
   visitGenerative(constants.GenerativeConstantConstructor constructor, arg) {
   }
 
   @override
   visitRedirectingFactory(
       constants.RedirectingFactoryConstantConstructor constructor, arg) {
   }
 
   @override
@@ skipping 232 matching lines @@
 
 class TreeVisitor1 extends tree_ir.ExpressionVisitor1
                       with tree_ir.StatementVisitor1 {
   noSuchMethod(inv) {}
 }
 
 useTreeVisitors() {
   new TreeVisitor1().visitExpression(null, null);
   new TreeVisitor1().visitStatement(null, null);
 }