dart2js cps: Compile some loops as 'for' loops.

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 39 matching lines @@
 
 main() {
   for (int i = 0; foo(true); i = foo(i)) {
     print(1);
     if (foo(false)) break;
   }
   print(2);
 }""", """
 function() {
   var i = 0;
-  while (V.foo(true) === true) {
+  for (; V.foo(true) === true; i = V.foo(i)) {
     P.print(1);
     if (V.foo(false) === true)
       break;
-    i = V.foo(i);
   }
   P.print(2);
 }"""),
 const TestEntry("""
 foo(a) => a;
 
 main() {
  if (foo(true)) {
    print(1);
  } else {
@@ skipping 54 matching lines @@
 }"""),
   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], $length = list.length, i = 0;
-  while (i < list.length) {
+  for (; i < list.length; i = i + 1) {
     P.print(list[i]);
     if ($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) {
+  for (; i < xs.length; i = i + 1, i1 = i1 + 1) {
     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);
 }