dart2js cps: Rewrite mutable variables to continuation parameters.

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 109 matching lines @@
   if (foo()) {
     print('bad');
   } else {
     print('good');
   }
 }""","""
 function() {
   V.foo();
   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], $length = list.length, i = 0;
+  while (i < list.length) {
+    P.print(list[i]);
+    if ($length !== list.length)
+      H.throwConcurrentModificationError(list);
+    i = i + 1;
+  }
+}"""),
+  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"], $length = xs.length, length1 = ys.length, i, i1, current, current1;
+  if ($length !== xs.length)
+    H.throwConcurrentModificationError(xs);
+  i = 0;
+  i1 = 0;
+  while (i < xs.length) {
+    current = xs[i];
+    if (length1 !== ys.length)
+      H.throwConcurrentModificationError(ys);
+    if (!(i1 < ys.length))
+      break;
+    current1 = ys[i1];
+    P.print(current);
+    P.print(current1);
+    if ($length !== xs.length)
+      H.throwConcurrentModificationError(xs);
+    i = i + 1;
+    i1 = i1 + 1;
+  }
+}"""),
 ];
 
 void main() {
   runTests(tests);
 }