Fix annotation of generic method invocations in Fasta inference tests.

pkg/front_end/testcases/inference/future_then_conditional_6.dart

Index: pkg/front_end/testcases/inference/future_then_conditional_6.dart
diff --git a/pkg/front_end/testcases/inference/future_then_conditional_6.dart b/pkg/front_end/testcases/inference/future_then_conditional_6.dart
index 1357ecf2f8f2a44e9982d30cfa63a0b48d3d5751..2ce8cc257e2d5c0e2f593685a3a135ce668f4c7f 100644
--- a/pkg/front_end/testcases/inference/future_then_conditional_6.dart
+++ b/pkg/front_end/testcases/inference/future_then_conditional_6.dart
@@ -16,20 +16,20 @@ class MyFuture<T> implements Future<T> {
 
 void main() {
   Future<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 Future<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 Future<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 Future<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