Set MethodInvocation.interfaceTarget during type inference.

pkg/front_end/testcases/inference/future_then_upwards_3.dart

Index: pkg/front_end/testcases/inference/future_then_upwards_3.dart
diff --git a/pkg/front_end/testcases/inference/future_then_upwards_3.dart b/pkg/front_end/testcases/inference/future_then_upwards_3.dart
index f24c958a32388cf0af84b68c0479730ca3ff7147..3c7f6947abc52a940f4bebe2e468e861da2e6707 100644
--- a/pkg/front_end/testcases/inference/future_then_upwards_3.dart
+++ b/pkg/front_end/testcases/inference/future_then_upwards_3.dart
@@ -15,14 +15,17 @@ class MyFuture<T> implements Future<T> {
 }
 
 void main() {
-  var /*@type=Future<double>*/ f = foo(). /*@typeArgs=double*/ then(
-      /*@returnType=double*/ (/*@type=dynamic*/ _) => 2.3);
+  var /*@type=Future<double>*/ f =
+      foo(). /*@typeArgs=double*/ /*@target=Future::then*/ then(
+          /*@returnType=double*/ (/*@type=dynamic*/ _) => 2.3);
   Future<int> f2 = /*error:INVALID_ASSIGNMENT*/ /*@promotedType=none*/ f;
 
   // The unnecessary cast is to illustrate that we inferred <double> for
   // the generic type args, even though we had a return type context.
-  Future<num> f3 = /*info:UNNECESSARY_CAST*/ foo(). /*@typeArgs=double*/ then(
-      /*@returnType=double*/ (/*@type=dynamic*/ _) => 2.3) as Future<double>;
+  Future<num> f3 = /*info:UNNECESSARY_CAST*/ foo()
+          . /*@typeArgs=double*/ /*@target=Future::then*/ then(
+              /*@returnType=double*/ (/*@type=dynamic*/ _) => 2.3)
+      as Future<double>;
 }
 
 Future foo() => new Future<int>.value(1);