dart2js cps: Introduce some built-in operators in type propagation.

tests/compiler/dart2js/js_backend_cps_ir_closures_test.dart

Index: tests/compiler/dart2js/js_backend_cps_ir_closures_test.dart
diff --git a/tests/compiler/dart2js/js_backend_cps_ir_closures_test.dart b/tests/compiler/dart2js/js_backend_cps_ir_closures_test.dart
index d4459d7cfe2d365d0ca5d832fdde232ffb84b981..d68f50aba36319c803506d54ab1410464dd5b02b 100644
--- a/tests/compiler/dart2js/js_backend_cps_ir_closures_test.dart
+++ b/tests/compiler/dart2js/js_backend_cps_ir_closures_test.dart
@@ -52,10 +52,10 @@ main() {
 """,
 r"""
 function() {
-  var _box_0 = {}, a, x;
+  var _box_0 = {}, a;
   _box_0._captured_x_0 = 122;
   a = new V.main_closure(_box_0);
-  _box_0._captured_x_0 = J.getInterceptor$ns(x = _box_0._captured_x_0).$add(x, 1);
+  _box_0._captured_x_0 = _box_0._captured_x_0 + 1;
   P.print(a.call$0());
   return null;
 }"""),
@@ -73,10 +73,10 @@ main() {
 """,
 r"""
 function() {
-  var _box_0 = {}, a, x;
+  var _box_0 = {}, a;
   _box_0._captured_x_0 = 122;
   a = new V.main_closure(_box_0);
-  _box_0._captured_x_0 = J.getInterceptor$ns(x = _box_0._captured_x_0).$add(x, 1);
+  _box_0._captured_x_0 = _box_0._captured_x_0 + 1;
   P.print(a.call$0().call$0());
   return null;
 }"""),
@@ -93,7 +93,7 @@ main() {
 r"""
 function() {
   var a = null, i = 0;
-  while (P.identical(J.getInterceptor$n(i).$lt(i, 10), true)) {
+  while (J.getInterceptor$n(i).$lt(i, 10)) {
     a = new V.main_closure(i);
     i = J.getInterceptor$ns(i).$add(i, 1);
   }