Move "null2" getter from ConstantVisitor to TypeProvider.

pkg/analyzer/lib/src/generated/testing/test_type_provider.dart

Index: pkg/analyzer/lib/src/generated/testing/test_type_provider.dart
diff --git a/pkg/analyzer/lib/src/generated/testing/test_type_provider.dart b/pkg/analyzer/lib/src/generated/testing/test_type_provider.dart
index a7de395208940b47330fac842ca5d4c38ad6b690..6824459c4b05da373143d4053e0d30ec7def9e7b 100644
--- a/pkg/analyzer/lib/src/generated/testing/test_type_provider.dart
+++ b/pkg/analyzer/lib/src/generated/testing/test_type_provider.dart
@@ -7,6 +7,7 @@
 
 library engine.testing.test_type_provider;
 
+import 'package:analyzer/src/generated/constant.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/resolver.dart';
 import 'package:analyzer/src/generated/testing/element_factory.dart';
@@ -92,6 +93,11 @@ class TestTypeProvider implements TypeProvider {
   InterfaceType _mapType;
 
   /**
+   * An shared object representing the value 'null'.
+   */
+  DartObjectImpl _nullObject;
+
+  /**
    * The type representing the built-in type 'Null'.
    */
   InterfaceType _nullType;
@@ -324,6 +330,14 @@ class TestTypeProvider implements TypeProvider {
   }
 
   @override
+  DartObjectImpl get nullObject {
+    if (_nullObject == null) {
+      _nullObject = new DartObjectImpl(nullType, NullState.NULL_STATE);
+    }
+    return _nullObject;
+  }
+
+  @override
   InterfaceType get nullType {
     if (_nullType == null) {
       _nullType = ElementFactory.classElement2("Null").type;