dart2js cps_ir: propagate constant field values

pkg/compiler/lib/src/cps_ir/type_propagation.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.type_propagation;
 
 import 'optimizers.dart';
 
 import '../closure.dart' show
     ClosureClassElement;
 import '../common.dart';
@@ skipping 3009 matching lines @@
       // TODO(asgerf): Add the NullInterceptor when it enables us to
       //               propagate an assignment.
       setValue(node, nonConstant());
     } else {
       setValue(node, nonConstant(typeSystem.nonNullType));
     }
   }
 
   void visitGetField(GetField node) {
     node.objectIsNotNull = getValue(node.object.definition).isDefinitelyNotNull;
-    setValue(node, nonConstant(typeSystem.getFieldType(node.field)));
+    setValue(node, lattice.fromMask(typeSystem.getFieldType(node.field)));
   }
 
   void visitSetField(SetField node) {}
 
   void visitCreateBox(CreateBox node) {
     setValue(node, nonConstant(typeSystem.nonNullType));
   }
 
   void visitCreateInstance(CreateInstance node) {
     setValue(node, nonConstant(typeSystem.nonNullExact(node.classElement.declaration)));
@@ skipping 189 matching lines @@
   processLetPrim(LetPrim node) {
     node.primitive.type = null;
     values[node.primitive] = null;
   }
 
   processLetMutable(LetMutable node) {
     node.variable.type = null;
     values[node.variable] = null;
   }
 }