Make `this` available in closures if a type variable is used as expression.

tests/language/closure_type_variable_test.dart

Index: tests/language/closure_type_variable_test.dart
diff --git a/tests/language/generic_is_check_test.dart b/tests/language/closure_type_variable_test.dart
similarity index 61%
copy from tests/language/generic_is_check_test.dart
copy to tests/language/closure_type_variable_test.dart
index 4e13c1f32e1720dd8c1fddf3daa52c43fca625c5..4f73267c7d8af37ade37f559fdade6c550d3e8dc 100644
--- a/tests/language/generic_is_check_test.dart
+++ b/tests/language/closure_type_variable_test.dart
@@ -2,12 +2,15 @@
 // 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.
 
+// Test that the type argument is available inside a closure.
+
 class A<T> {
-  foo() => this is A<int>;
+  foo() {
+    bar() => T;
+    return bar();
+  }
 }
 
 main() {
-  Expect.isTrue(new A().foo());
-  Expect.isTrue(new A<int>().foo());
-  Expect.isFalse(new A<String>().foo());
+  Expect.equals(new A<int>().foo(), int);
 }