Use type argument for abstract values.

pkg/compiler/lib/src/cps_ir/optimizers.dart

 // Copyright (c) 2014, 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.cps_ir.optimizers;
 
 import '../constants/expressions.dart' show
     ConstantExpression,
     PrimitiveConstantExpression;
 import '../constants/values.dart';
 import '../dart_types.dart' as types;
 import '../dart2jslib.dart' as dart2js;
 import '../tree/tree.dart' show LiteralDartString;
 import '../util/util.dart';
 import 'cps_ir_nodes.dart';
 import '../types/types.dart' show TypeMask, TypesTask;
+import '../core_types.dart' show CoreTypes;
 import '../types/constants.dart' show computeTypeMask;
 import '../elements/elements.dart' show ClassElement, Element, Entity,
     FieldElement, FunctionElement, ParameterElement;
 import '../dart2jslib.dart' show ClassWorld;
 
 part 'type_propagation.dart';
 part 'redundant_phi.dart';
 part 'shrinking_reductions.dart';
 
 /// An optimization pass over the CPS IR.
@@ skipping 18 matching lines @@
 
   void rewriteConstructorDefinition(ConstructorDefinition root) {
     if (root.isAbstract) return;
     rewriteExecutableDefinition(root);
   }
   void rewriteFieldDefinition(FieldDefinition root) {
     if (!root.hasInitializer) return;
     rewriteExecutableDefinition(root);
   }
 }