dart2js cps: Add a pass for eliminating bounds checks.

tests/compiler/dart2js/js_backend_cps_ir_control_flow_test.dart

Index: tests/compiler/dart2js/js_backend_cps_ir_control_flow_test.dart
diff --git a/tests/compiler/dart2js/js_backend_cps_ir_control_flow_test.dart b/tests/compiler/dart2js/js_backend_cps_ir_control_flow_test.dart
index d3340b4cd07e709f0f9af94a49a1a1dd0960b49d..2365d4fe979df3c39789717bf2b4606ee0cbbecb 100644
--- a/tests/compiler/dart2js/js_backend_cps_ir_control_flow_test.dart
+++ b/tests/compiler/dart2js/js_backend_cps_ir_control_flow_test.dart
@@ -155,11 +155,7 @@ main() {
   }
 }""",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)