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 cc37c089a8f62beb93079f0887623d7abba189f1..0a887b2b3d107c744ac6238d1ab730af6437de7e 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
@@ -151,11 +151,7 @@ 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)