kernel->ssa: implement top-level getters and setters

tests/compiler/dart2js/kernel/getters_setters_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() {
+  group('compile getters with kernel', () {
+    test('top-level', () {
+      String code = '''
+int get foo => 1;
+main() => foo;
+''';
+      return check(code);
+    });
+
+    test('static', () {
+      String code = '''
+class A {
+  static int get foo => 1;
+}
+main() => A.foo;
+''';
+      return check(code);
+    });
+  });
+
+  group('compile setters with kernel', () {
+    test('top-level', () {
+      String code = '''
+set foo(int newFoo) {
+  // do nothing
+}
+main() {
+  foo = 1;
+}''';
+      return check(code);
+    });
+
+    test('static', () {
+      String code = '''
+class A {
+  static set foo(int newFoo) {
+    // do nothing
+  }
+}
+main() {
+  A.foo = 1;
+}
+''';
+      return check(code);
+    });
+  });
+}