Fix window restore behaviour on Mac.

chrome/browser/app_controller_cppsafe_mac.h

+// Copyright (c) 2009 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.
+
+#ifndef CHROME_BROWSER_APP_CONTROLLER_CPPSAFE_MAC_H_
+#define CHROME_BROWSER_APP_CONTROLLER_CPPSAFE_MAC_H_
+
+// We declare this in a separate file that is safe for including in C++ code.
+
+namespace app_controller_mac {
+
+// True if we are currently handling an IDC_NEW_{TAB,WINDOW} command. Used in
+// SessionService::Observe() to get around windows/linux and mac having
+// different models of application lifetime.
+bool IsOpeningNewWindow();
+
+}  // namespace app_controller_mac
+
+#endif  // CHROME_BROWSER_APP_CONTROLLER_CPPSAFE_MAC_H_