tree-ir: Treat getInterceptor and identical as effectively constant.

tests/compiler/dart2js/js_backend_cps_ir_interceptors_test.dart

Index: tests/compiler/dart2js/js_backend_cps_ir_interceptors_test.dart
diff --git a/tests/compiler/dart2js/js_backend_cps_ir_interceptors_test.dart b/tests/compiler/dart2js/js_backend_cps_ir_interceptors_test.dart
index 98e14d5136b736015384d82ffb941625327ab767..6cb5490151229c9601ac72a6e40173337966abfe 100644
--- a/tests/compiler/dart2js/js_backend_cps_ir_interceptors_test.dart
+++ b/tests/compiler/dart2js/js_backend_cps_ir_interceptors_test.dart
@@ -36,28 +36,19 @@ main() {
 }""",
 r"""
 function() {
-  var l = ["hest", ["h", "e", "s", "t"]], i, v0, x, j;
+  var l = ["hest", ["h", "e", "s", "t"]], i, x, j;
   P.print(J.getInterceptor$as(l).get$length(l));
   i = 0;
-  L0:
-    while (true) {
-      v0 = J.getInterceptor$as(l).get$length(l);
-      if (P.identical(J.getInterceptor$n(i).$lt(i, v0), true)) {
-        x = J.getInterceptor$as(l).$index(l, i);
-        j = 0;
-        while (true) {
-          v0 = J.getInterceptor$as(x).get$length(x);
-          if (P.identical(J.getInterceptor$n(j).$lt(j, v0), true)) {
-            P.print(J.getInterceptor$as(x).$index(x, j));
-            j = J.getInterceptor$ns(j).$add(j, 1);
-          } else {
-            i = J.getInterceptor$ns(i).$add(i, 1);
-            continue L0;
-          }
-        }
-      } else
-        return null;
+  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 (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;
 }"""),
 ];