Gtk3: Fix gn_all compile

remoting/host/continue_window_linux.cc

 // Copyright (c) 2012 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 "remoting/host/continue_window.h"
 
 #include <gtk/gtk.h>
 
 #include "base/compiler_specific.h"
 #include "base/logging.h"
@@ skipping 52 matching lines @@
   if (continue_window_) {
     gtk_widget_destroy(continue_window_);
     continue_window_ = nullptr;
   }
 }
 
 void ContinueWindowGtk::CreateWindow() {
   DCHECK(CalledOnValidThread());
   DCHECK(!continue_window_);
 
+  GtkDialogFlags flags = GTK_DIALOG_MODAL;
+#if GTK_MAJOR_VERSION == 2
+  flags = static_cast<GtkDialogFlags>(flags | GTK_DIALOG_NO_SEPARATOR);
+#endif
   continue_window_ = gtk_dialog_new_with_buttons(
       l10n_util::GetStringUTF8(IDS_PRODUCT_NAME).c_str(),
       nullptr,
-      static_cast<GtkDialogFlags>(GTK_DIALOG_MODAL | GTK_DIALOG_NO_SEPARATOR),
+      flags,
       l10n_util::GetStringUTF8(IDS_STOP_SHARING_BUTTON).c_str(),
       GTK_RESPONSE_CANCEL,
       l10n_util::GetStringUTF8(IDS_CONTINUE_BUTTON).c_str(),
       GTK_RESPONSE_OK,
       nullptr);
 
   gtk_dialog_set_default_response(GTK_DIALOG(continue_window_),
                                   GTK_RESPONSE_OK);
   gtk_window_set_resizable(GTK_WINDOW(continue_window_), FALSE);
 
@@ skipping 28 matching lines @@
 
   HideUi();
 }
 
 // static
 std::unique_ptr<HostWindow> HostWindow::CreateContinueWindow() {
   return base::MakeUnique<ContinueWindowGtk>();
 }
 
 }  // namespace remoting