Use ConstExp for storing constants.

sdk/lib/_internal/compiler/implementation/inferrer/type_graph_inferrer.dart

Index: sdk/lib/_internal/compiler/implementation/inferrer/type_graph_inferrer.dart
diff --git a/sdk/lib/_internal/compiler/implementation/inferrer/type_graph_inferrer.dart b/sdk/lib/_internal/compiler/implementation/inferrer/type_graph_inferrer.dart
index f7b6761f2f8ad31665d05170db5fa92f96a3cb74..71cc52b9f8ac9e09ab409eb5e6226df5906915f7 100644
--- a/sdk/lib/_internal/compiler/implementation/inferrer/type_graph_inferrer.dart
+++ b/sdk/lib/_internal/compiler/implementation/inferrer/type_graph_inferrer.dart
@@ -5,6 +5,7 @@
 library type_graph_inferrer;
 
 import 'dart:collection' show Queue, IterableBase;
+import '../cps_ir/const_expression.dart';
 import '../dart_types.dart' show DartType, InterfaceType, TypeKind;
 import '../elements/elements.dart';
 import '../tree/tree.dart' as ast show DartString, Node;
@@ -742,9 +743,10 @@ class TypeGraphInferrerEngine
           if (type is! ListTypeInformation && type is! MapTypeInformation) {
             // For non-container types, the constant handler does
             // constant folding that could give more precise results.
-            Constant value = compiler.backend.constants
+            ConstExp constant = compiler.backend.constants
                 .getConstantForVariable(element);
-            if (value != null) {
+            if (constant != null) {
+              Constant value = constant.value;
               if (value.isFunction) {
                 FunctionConstant functionConstant = value;
                 type = types.allocateClosure(node, functionConstant.element);