Handle parenthesized expression in type promotion.

tests/language/type_promotion_parameter_test.dart

 // Copyright (c) 2013, 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.
 
 // Test type promotion of parameters.
 
 class A {
   var a = "a";
 }
 class B extends A {
@@ skipping 172 matching lines @@
       && a.c == ""
       && a.d == "" /// 51: static type warning
       ) {
     print(a.a);
     print(a.b);
     print(a.c);
     print(a.d); /// 52: static type warning
   }
   if ((a is B)) {
     print(a.a);
-    print(a.b); /// 53: static type warning
+    print(a.b);
     print(a.c); /// 54: static type warning
     print(a.d); /// 55: static type warning
   }
+  if ((a is B && (a) is C) && a is B) {
+    print(a.a);
+    print(a.b);
+    print(a.c);
+    print(a.d); /// 56: static type warning
+  }
 }