Add DartTypes to abstract Types.

pkg/compiler/lib/src/constant_system_dart.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.
 
 part of dart2js;
 
 const DART_CONSTANT_SYSTEM = const DartConstantSystem();
 
 class BitNotOperation implements UnaryOperation {
   final String name = '~';
@@ skipping 384 matching lines @@
                              List<ConstantValue> values) {
     return new MapConstantValue(type, keys, values);
   }
 
   bool isInt(ConstantValue constant) => constant.isInt;
   bool isDouble(ConstantValue constant) => constant.isDouble;
   bool isString(ConstantValue constant) => constant.isString;
   bool isBool(ConstantValue constant) => constant.isBool;
   bool isNull(ConstantValue constant) => constant.isNull;
 
-  bool isSubtype(Compiler compiler, DartType s, DartType t) {
-    return compiler.types.isSubtype(s, t);
+  bool isSubtype(DartTypes types, DartType s, DartType t) {
+    return types.isSubtype(s, t);
   }
 }