Access ConstantSystem through ClosedWorld.

pkg/compiler/lib/src/ssa/graph_builder.dart

Index: pkg/compiler/lib/src/ssa/graph_builder.dart
diff --git a/pkg/compiler/lib/src/ssa/graph_builder.dart b/pkg/compiler/lib/src/ssa/graph_builder.dart
index 278ed73866aa8668f256a4fa70f2ce10770b6ef4..35566b869c1e59319e9d5e7a8b6bd96f5a66264b 100644
--- a/pkg/compiler/lib/src/ssa/graph_builder.dart
+++ b/pkg/compiler/lib/src/ssa/graph_builder.dart
@@ -6,6 +6,7 @@ import '../closure.dart';
 import '../common.dart';
 import '../common/codegen.dart' show CodegenRegistry;
 import '../compiler.dart';
+import '../constants/constant_system.dart';
 import '../dart_types.dart';
 import '../elements/elements.dart';
 import '../io/source_information.dart';
@@ -82,7 +83,7 @@ abstract class GraphBuilder {
 
   /// Pushes a boolean checking [expression] against null.
   pushCheckNull(HInstruction expression) {
-    push(new HIdentity(expression, graph.addConstantNull(compiler), null,
+    push(new HIdentity(expression, graph.addConstantNull(closedWorld), null,
         closedWorld.commonMasks.boolType));
   }
 
@@ -292,7 +293,8 @@ class ReifiedTypeRepresentationBuilder
     List<String> names = type.namedParameters;
     for (int index = 0; index < names.length; index++) {
       ast.DartString dartString = new ast.DartString.literal(names[index]);
-      inputs.add(builder.graph.addConstantString(dartString, builder.compiler));
+      inputs.add(
+          builder.graph.addConstantString(dartString, builder.closedWorld));
       namedParameterTypes[index].accept(this, builder);
       inputs.add(builder.pop());
     }