dart2js cps: Add a pass for eliminating bounds checks.

tests/compiler/dart2js/js_backend_cps_ir_control_flow_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 control flow statements.
 
 library control_flow_tests;
 
 import 'js_backend_cps_ir.dart';
 
@@ skipping 137 matching lines @@
   const TestEntry("""
 main() {
   var xs = ['x', 'y', 'z'], ys = ['A', 'B', 'C'];
   var xit = xs.iterator, yit = ys.iterator;
   while (xit.moveNext() && yit.moveNext()) {
     print(xit.current);
     print(yit.current);
   }
 }""",r"""
 function() {
-  var xs = ["x", "y", "z"], ys = ["A", "B", "C"], $length = xs.length, length1 = ys.length, i, i1, current, current1;
-  if ($length !== xs.length)
-    H.throwConcurrentModificationError(xs);
-  i = 0;
-  i1 = 0;
+  var xs = ["x", "y", "z"], ys = ["A", "B", "C"], $length = xs.length, length1 = ys.length, i = 0, i1 = 0, current, current1;
   for (; i < xs.length; i = i + 1, i1 = i1 + 1) {
     current = xs[i];
     if (length1 !== ys.length)
       H.throwConcurrentModificationError(ys);
     if (!(i1 < ys.length))
       break;
     current1 = ys[i1];
     P.print(current);
     P.print(current1);
     if ($length !== xs.length)
       H.throwConcurrentModificationError(xs);
   }
 }"""),
 ];
 
 void main() {
   runTests(tests);
 }