Fix annotation of generic method invocations in Fasta inference tests.

pkg/front_end/testcases/inference/future_then_conditional_2.dart

Index: pkg/front_end/testcases/inference/future_then_conditional_2.dart
diff --git a/pkg/front_end/testcases/inference/future_then_conditional_2.dart b/pkg/front_end/testcases/inference/future_then_conditional_2.dart
index 46a2bcd2ff0f05cc45dedcfd02d4cb20377d06e2..d08e44a54c73af26fb607871746bc2fcdf1745f7 100644
--- a/pkg/front_end/testcases/inference/future_then_conditional_2.dart
+++ b/pkg/front_end/testcases/inference/future_then_conditional_2.dart
@@ -16,20 +16,20 @@ class MyFuture<T> implements Future<T> {
 
 void main() {
   MyFuture<bool> f;
-  Future<int> t1 = /*@promotedType=none*/ f.then(
+  Future<int> t1 = /*@promotedType=none*/ f. /*@typeArgs=int*/ then(
       /*@returnType=Future<int>*/ (/*@type=bool*/ x) async =>
           /*@promotedType=none*/ x ? 2 : await new MyFuture<int>.value(3));
-  Future<int> t2 = /*@promotedType=none*/ f
-      .then(/*@returnType=Future<int>*/ (/*@type=bool*/ x) async {
+  Future<int> t2 = /*@promotedType=none*/ f. /*@typeArgs=int*/ then(
+      /*@returnType=Future<int>*/ (/*@type=bool*/ x) async {
     return /*info:DOWN_CAST_COMPOSITE*/ await /*@promotedType=none*/ x
         ? 2
         : new MyFuture<int>.value(3);
   });
-  Future<int> t5 = /*@promotedType=none*/ f.then(
+  Future<int> t5 = /*@promotedType=none*/ f. /*@typeArgs=int*/ then(
       /*info:INFERRED_TYPE_CLOSURE,error:INVALID_CAST_FUNCTION_EXPR*/
       /*@returnType=Object*/ (/*@type=bool*/ x) =>
           /*@promotedType=none*/ x ? 2 : new MyFuture<int>.value(3));
-  Future<int> t6 = /*@promotedType=none*/ f.then(
+  Future<int> t6 = /*@promotedType=none*/ f. /*@typeArgs=int*/ then(
       /*@returnType=FutureOr<int>*/ (/*@type=bool*/ x) {
     return /*info:DOWN_CAST_COMPOSITE*/ /*@promotedType=none*/ x
         ? 2