Add type inference for `this` expressions.

pkg/front_end/testcases/inference/this_reference.dart

Index: pkg/front_end/testcases/inference/this_reference.dart
diff --git a/pkg/front_end/testcases/inference/this_reference.dart b/pkg/front_end/testcases/inference/this_reference.dart
new file mode 100644
index 0000000000000000000000000000000000000000..36bd0b4a1c28f593c4cf2276c788d1864c8c2fda
--- /dev/null
+++ b/pkg/front_end/testcases/inference/this_reference.dart
@@ -0,0 +1,14 @@
+// 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<T> {
+  void f() {
+    var /*@type=C<C::T>*/ x = this;
+  }
+}
+
+main() {}