dart2dart: Test cases for better code coverage in dart_tree rewritings.

tests/language/rewrite_while_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.
+
+import "package:expect/expect.dart";
+
+f1(b) {
+  while (b)
+    return 1;
+
+  return 2;
+}
+
+f2(b) {
+  while (b) {
+    return 1;
+  }
+  return 2;
+}
+
+f3(n) {
+  var i = 0;
+  while (i < n) {
+    i = i + 1;
+  }
+  return i;
+}
+
+main() {
+    Expect.equals(1, f1(true));
+    Expect.equals(2, f1(false));
+    Expect.equals(1, f2(true));
+    Expect.equals(2, f2(false));
+    Expect.equals(0, f3(-2));
+    Expect.equals(0, f3(-1));
+    Expect.equals(0, f3(0));
+    Expect.equals(1, f3(1));
+    Expect.equals(2, f3(2));
+}