Fix inferInvocation for top level inference.

pkg/front_end/testcases/inference/downwards_inference_inside_top_level_2.dart

+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/*@testedFeatures=inference*/
+library test;
+
+class A<T> {
+  A(T x);
+}
+
+var /*@topType=List<A<int>>*/ t1 = <A<int>>[new /*@typeArgs=int*/ A(1)];
+var /*@topType=List<A<dynamic>>*/ t2 = /*@typeArgs=A<dynamic>*/ [
+  new
+      /*error:TOP_LEVEL_TYPE_ARGUMENTS*/ /*@typeArgs=dynamic*/ A(2)
+];
+
+main() {}