Add a getter to TypeProvider for Future<Null>.

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 9a719d4acb92ff7b60d8fa3da9376fc47f2ae17d..099e50c143bb0413f9397756f657ce9147c71d68 100644
--- a/pkg/analyzer/lib/src/generated/testing/test_type_provider.dart
+++ b/pkg/analyzer/lib/src/generated/testing/test_type_provider.dart
@@ -47,7 +47,12 @@ class TestTypeProvider implements TypeProvider {
   InterfaceType _functionType;
 
   /**
-   * THe type representing the built-in type 'Future'
+   * The type representing 'Future<Null>'
+   */
+  InterfaceType _futureNullType;
+
+  /**
+   * The type representing the built-in type 'Future'
    */
   InterfaceType _futureType;
 
@@ -177,6 +182,14 @@ class TestTypeProvider implements TypeProvider {
   }
 
   @override
+  InterfaceType get futureNullType {
+    if (_futureNullType == null) {
+      _futureNullType = futureType.substitute4(<DartType>[nullType]);
+    }
+    return _futureNullType;
+  }
+
+  @override
   InterfaceType get futureType {
     if (_futureType == null) {
       _futureType = ElementFactory.classElement2("Future", ["T"]).type;