dart2js cps_ir: propagate constant field values

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

Index: pkg/compiler/lib/src/cps_ir/type_propagation.dart
diff --git a/pkg/compiler/lib/src/cps_ir/type_propagation.dart b/pkg/compiler/lib/src/cps_ir/type_propagation.dart
index 0cf049e4765b8cfeaf4a319d98e25bf19a6df47c..1e6b1188c63b89d7289363238ef2f2446dcbb535 100644
--- a/pkg/compiler/lib/src/cps_ir/type_propagation.dart
+++ b/pkg/compiler/lib/src/cps_ir/type_propagation.dart
@@ -3027,7 +3027,7 @@ class TypePropagationVisitor implements Visitor {
 
   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) {}