Do not use the namer for naming closure elements.

tests/compiler/dart2js/js_backend_cps_ir_closures_test.dart

 // Copyright (c) 2014, 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.
 // VMOptions=-DUSE_CPS_IR=true
 
 // Tests of closures.
 
 library closures_test;
 
 import 'js_backend_cps_ir.dart';
 
 const List<TestEntry> tests = const [
   const TestEntry("""
 main(x) {
   a() {
     return x;
   }
   x = x + '1';
   print(a());
 }
 """,
 r"""
 function(x) {
-  var box_0, a;
-  box_0 = {};
-  box_0.x_0 = x;
-  a = new V.main_a(box_0);
-  x = box_0.x_0;
-  box_0.x_0 = J.getInterceptor$ns(x).$add(x, "1");
+  var _box_0, a;
+  _box_0 = {};
+  _box_0._captured_x_0 = x;
+  a = new V.main_a(_box_0);
+  x = _box_0._captured_x_0;
+  _box_0._captured_x_0 = J.getInterceptor$ns(x).$add(x, "1");
   P.print(a.call$0());
   return null;
 }"""),
 
   const TestEntry("""
 main(x) {
   a() {
     return x;
   }
   print(a());
 }
 """,
 r"""
 function(x) {
   P.print(new V.main_a(x).call$0());
   return null;
 }"""),
 
   const TestEntry("""
 main() {
   var x = 122;
   var a = () => x;
   x = x + 1;
   print(a());
 }
 """,
 r"""
 function() {
-  var box_0, a, x;
-  box_0 = {};
-  box_0.x_0 = 122;
-  a = new V.main_closure(box_0);
-  x = box_0.x_0;
-  box_0.x_0 = J.getInterceptor$ns(x).$add(x, 1);
+  var _box_0, a, x;
+  _box_0 = {};
+  _box_0._captured_x_0 = 122;
+  a = new V.main_closure(_box_0);
+  x = _box_0._captured_x_0;
+  _box_0._captured_x_0 = J.getInterceptor$ns(x).$add(x, 1);
   P.print(a.call$0());
   return null;
 }"""),
 
   const TestEntry("""
 main() {
   var x = 122;
   var a = () {
     var y = x;
     return () => y;
   };
   x = x + 1;
   print(a()());
 }
 """,
 r"""
 function() {
-  var box_0, a, x;
-  box_0 = {};
-  box_0.x_0 = 122;
-  a = new V.main_closure(box_0);
-  x = box_0.x_0;
-  box_0.x_0 = J.getInterceptor$ns(x).$add(x, 1);
+  var _box_0, a, x;
+  _box_0 = {};
+  _box_0._captured_x_0 = 122;
+  a = new V.main_closure(_box_0);
+  x = _box_0._captured_x_0;
+  _box_0._captured_x_0 = J.getInterceptor$ns(x).$add(x, 1);
   P.print(a.call$0().call$0());
   return null;
 }"""),
 
   const TestEntry("""
 main() {
   var a;
   for (var i=0; i<10; i++) {
     a = () => i;
   }
@@ skipping 24 matching lines @@
 """,
 r"""
 function() {
   return new V.A_b_closure(this);
 }"""),
 ];
 
 void main() {
   runTests(tests);
 }