Add type inference for null-aware method invocations.

pkg/front_end/testcases/inference/null_aware_method_invocation.dart

Index: pkg/front_end/testcases/inference/null_aware_method_invocation.dart
diff --git a/pkg/front_end/testcases/inference/null_aware_method_invocation.dart b/pkg/front_end/testcases/inference/null_aware_method_invocation.dart
new file mode 100644
index 0000000000000000000000000000000000000000..7ff4643d5bb339e53275c3b41d2d3796fdd9ba69
--- /dev/null
+++ b/pkg/front_end/testcases/inference/null_aware_method_invocation.dart
@@ -0,0 +1,16 @@
+// 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 C {
+  int f() => null;
+}
+
+g(C c) {
+  var /*@type=int*/ x = c?. /*@target=C::f*/ f();
+}
+
+main() {}