Fix annotation of generic method invocations in Fasta inference tests.

pkg/front_end/testcases/inference/future_then_conditional.dart

Index: pkg/front_end/testcases/inference/future_then_conditional.dart
diff --git a/pkg/front_end/testcases/inference/future_then_conditional.dart b/pkg/front_end/testcases/inference/future_then_conditional.dart
index 19355558d6e93b86ee9494d2e7ecdb216da0bbda..ab579123bcb32ce493b9e87a3db0906e8ccbbb68 100644
--- a/pkg/front_end/testcases/inference/future_then_conditional.dart
+++ b/pkg/front_end/testcases/inference/future_then_conditional.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 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(
       /*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