dart2js cps: Add a pass for eliminating bounds checks.

tests/compiler/dart2js/js_backend_cps_ir_operators_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.
 
 // Tests of operators.
 
 library operators_tests;
 
 import 'js_backend_cps_ir.dart';
 
@@ skipping 66 matching lines @@
 //}
 //"""),
 
 const TestEntry("""
 main() {
   var list = [1, 2, 3];
   list[1] = 6;
   print(list);
 }""", r"""
 function() {
-  var list = [1, 2, 3], v0 = 1;
-  if (v0 < 0 || v0 >= list.length)
-    H.ioore(list, v0);
-  list[v0] = 6;
+  var list = [1, 2, 3];
+  list[1] = 6;
   P.print(list);
 }"""),
 ];
 
 void main() {
   runTests(tests);
 }