dart2js cps: Type casts and related changes to type propagation.

tests/compiler/dart2js/js_backend_cps_ir_interceptors_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 interceptors.
 
 library interceptors_tests;
 
 import 'js_backend_cps_ir.dart';
 
@@ skipping 20 matching lines @@
     for (int j = 0; j < x.length; j++) {
       print(x[j]);
     }
   }
 }""",
 r"""
 function() {
   var l = ["hest", ["h", "e", "s", "t"]], i, x, j;
   P.print(J.getInterceptor$as(l).get$length(l));
   i = 0;
-  while (J.getInterceptor$n(i).$lt(i, J.getInterceptor$as(l).get$length(l))) {
+  while (P.identical(J.getInterceptor$n(i).$lt(i, J.getInterceptor$as(l).get$length(l)), true)) {
     x = J.getInterceptor$as(l).$index(l, i);
     j = 0;
-    while (J.getInterceptor$n(j).$lt(j, J.getInterceptor$as(x).get$length(x))) {
+    while (P.identical(J.getInterceptor$n(j).$lt(j, J.getInterceptor$as(x).get$length(x)), true)) {
       P.print(J.getInterceptor$as(x).$index(x, j));
       j = J.getInterceptor$ns(j).$add(j, 1);
     }
     i = J.getInterceptor$ns(i).$add(i, 1);
   }
   return null;
 }"""),
 ];
 
 
 void main() {
   runTests(tests);
 }