[Aura] Support always-on-top top level window.

ui/aura_shell/test/aura_shell_test_base.cc

+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ui/aura_shell/test/aura_shell_test_base.h"
+
+#include "ui/aura_shell/shell.h"
+
+namespace aura_shell {
+namespace test {
+
+AuraShellTestBase::AuraShellTestBase() {
+}
+
+AuraShellTestBase::~AuraShellTestBase() {
+}
+
+void AuraShellTestBase::SetUp() {
+  aura::test::AuraTestBase::SetUp();
+
+  // Creates Shell and hook with Desktop.
+  aura_shell::Shell::CreateInstance(NULL);
+}
+
+void AuraShellTestBase::TearDown() {
+  // Flush the message loop to finish pending release tasks.
+  RunAllPendingInMessageLoop();
+
+  // Tear down the shell.
+  aura_shell::Shell::DeleteInstanceForTesting();
+
+  aura::test::AuraTestBase::TearDown();
+}
+
+}  // namespace test
+}  // namespace aura_shell