dart2dart: Restore loops with conditions and updates in backend.

tests/language/rewrite_for_update_order.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.
 
 import "package:expect/expect.dart";
 
+var counter = 0;
 var global = 0;
 
-bar() {
-    global += 1;
-}
-baz() {
-    global += 100;
+test() {
+    ++counter;
+    return counter <= 2;
 }
 
-foo(b) {
-    var old_backend_was_used;
-    if (b ? false : true) {
-        bar();
-        bar();
-    } else {
-        baz();
-        baz();
+first() {
+    global = global + 1;
+}
+second() {
+    global = global * 2;
+}
+
+foo() {
+    while (test()) {
+        first();
+        second();
     }
 }
 
 main() {
-    foo(true);
-    Expect.equals(200, global);
-
-    foo(false);
-    Expect.equals(202, global);
+    foo();
+    Expect.equals(6, global);
 }