dart2js cps: Propagate container types for lists.

tests/compiler/dart2js/js_backend_cps_ir_control_flow_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 control flow statements.
 
 library control_flow_tests;
 
 import 'js_backend_cps_ir.dart';
 
@@ skipping 120 matching lines @@
   P.print("good");
 }"""),
   const TestEntry("""
 main() {
   var list = [1,2,3,4,5,6];
   for (var x in list) {
     print(x);
   }
 }""",r"""
 function() {
-  var list = [1, 2, 3, 4, 5, 6], $length = list.length, i = 0;
-  for (; i < list.length; i = i + 1) {
+  var list = [1, 2, 3, 4, 5, 6], i = 0;
+  for (; i < 6; i = i + 1)
     P.print(list[i]);
-    if ($length !== list.length)
-      H.throwConcurrentModificationError(list);
-  }
 }"""),
   const TestEntry("""
 main() {
   var xs = ['x', 'y', 'z'], ys = ['A', 'B', 'C'];
   var xit = xs.iterator, yit = ys.iterator;
   while (xit.moveNext() && yit.moveNext()) {
     print(xit.current);
     print(yit.current);
   }
 }""",r"""
 function() {
-  var xs = ["x", "y", "z"], ys = ["A", "B", "C"], $length = xs.length, length1 = ys.length, i = 0, i1 = 0, current, current1;
-  for (; i < xs.length; i = i + 1, i1 = i1 + 1) {
+  var xs = ["x", "y", "z"], ys = ["A", "B", "C"], i = 0, i1 = 0, current, current1;
+  for (; i < 3; i = i + 1, i1 = i1 + 1) {
     current = xs[i];
-    if (length1 !== ys.length)
-      H.throwConcurrentModificationError(ys);
-    if (!(i1 < ys.length))
+    if (!(i1 < 3))
       break;
     current1 = ys[i1];
     P.print(current);
     P.print(current1);
-    if ($length !== xs.length)
-      H.throwConcurrentModificationError(xs);
   }
 }"""),
 ];
 
 void main() {
   runTests(tests);
 }