Handle parenthesized expression in type promotion.

tests/language/type_promotion_closure_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 locals potentially mutated in closures.
 
 class A {
   var a = "a";
   A operator +(int i) => this;
 }
@@ skipping 12 matching lines @@
   var c = "";
   var d = "";
 }
 
 func(x) => true;
 
 void main() {
   test1();
   test2();
   test3();
+  test3a();
   test4();
   test5();
   test6();
+  test6a();
   test7();
   test8();
   test9();
   test10();
   test11();
   test12();
 }
 
 void test1() {
   A a = new E();
@@ skipping 26 matching lines @@
     print(a.a);
     print(a.b); /// 03: static type warning
     void foo() {
       a = new D();
     }
     print(a.a);
     print(a.b); /// 04: static type warning
   }
 }
 
+void test3a() {
+  A a = new E();
+  void foo() {
+    a = new D();
+  }
+  if ((((a)) is B)) {
+    print(a.a);
+    print(a.b); /// 15: static type warning
+    void foo() {
+      a = new D();
+    }
+    print(a.a);
+    print(a.b); /// 16: static type warning
+  }
+}
+
 void test4() {
   A a = new E();
   if (a is B) {
     func(() => a.b); /// 05: ok
     print(a.a);
     print(a.b);
   }
 }
 
 void test5() {
   A a = new E();
   if (a is B) {
     func(() => a.b); /// 06: static type warning
     print(a.a);
   }
   a = null;
 }
 
 void test6() {
   A a = new E();
   if (a is B) {
     func(() => a);
     print(a.a);
     print(a.b); /// 07: static type warning
   }
   a = null;
 }
 
+void test6a() {
+  A a = new E();
+  if (((a) is B)) {
+    func(() => a);
+    print(a.a);
+    print(a.b); /// 14: static type warning
+  }
+  a = null;
+}
+
 void test7() {
   A a = new E();
   if (a is B && func(() => a)) {
     print(a.a);
     print(a.b); /// 08: ok
   }
   a = null;
 }
 
 void test8() {
@@ skipping 32 matching lines @@
 
 void test12() {
   A a = new E();
   if (a is B) {
     func(() => a++);
     print(a.a);
     print(a.b); /// 13: static type warning
   }
   a = null;
 }