Set MethodInvocation.interfaceTarget during type inference.

pkg/front_end/testcases/inference/future_then_explicit_future.dart

Index: pkg/front_end/testcases/inference/future_then_explicit_future.dart
diff --git a/pkg/front_end/testcases/inference/future_then_explicit_future.dart b/pkg/front_end/testcases/inference/future_then_explicit_future.dart
index 6f49c38ddfe1f4bb8099130249ca764e9d7ed6f0..7559453532bc5792c753015140f0bb297cfe6b94 100644
--- a/pkg/front_end/testcases/inference/future_then_explicit_future.dart
+++ b/pkg/front_end/testcases/inference/future_then_explicit_future.dart
@@ -9,16 +9,17 @@ import "dart:async";
 
 m1() {
   Future<int> f;
-  var /*@type=Future<List<int>>*/ x = /*@promotedType=none*/ f.then<
-          Future<List<int>>>(
-      /*error:ARGUMENT_TYPE_NOT_ASSIGNABLE*/
-      /*@returnType=List<dynamic>*/ (/*@type=int*/ x) => /*@typeArgs=dynamic*/ []);
+  var /*@type=Future<List<int>>*/ x = /*@promotedType=none*/ f
+      . /*@target=Future::then*/ then<Future<List<int>>>(
+          /*error:ARGUMENT_TYPE_NOT_ASSIGNABLE*/
+          /*@returnType=List<dynamic>*/ (/*@type=int*/ x) => /*@typeArgs=dynamic*/ []);
   Future<List<int>> y = /*@promotedType=none*/ x;
 }
 
 m2() {
   Future<int> f;
-  var /*@type=Future<List<int>>*/ x = /*@promotedType=none*/ f.then<List<int>>(
-      /*@returnType=List<int>*/ (/*@type=int*/ x) => /*@typeArgs=int*/ []);
+  var /*@type=Future<List<int>>*/ x = /*@promotedType=none*/ f
+      . /*@target=Future::then*/ then<List<int>>(
+          /*@returnType=List<int>*/ (/*@type=int*/ x) => /*@typeArgs=int*/ []);
   Future<List<int>> y = /*@promotedType=none*/ x;
 }