kernel->ssa: Implement for-loops and while-loops

tests/compiler/dart2js/kernel/loops_test.dart

+// Copyright (c) 2016, 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:test/test.dart';
+
+import 'helper.dart' show check;
+
+main() {
+  test('for-loop', () {
+    String code = '''
+main() {
+  var a = 0;
+  for (var i = 0; i < 10; i++) {
+    a += i;
+  }
+  return a;
+}''';
+    return check(code);
+  });
+
+  test('while-loop', () {
+    String code = '''
+main() {
+  var a = 0;
+  while (a < 100) {
+    a *= 2;
+  }
+  return a;
+}''';
+    return check(code);
+  });
+}