Make File-Picker modal on Linux

ui/views/widget/desktop_aura/x11_desktop_handler.h

 // 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.
 
 #ifndef UI_VIEWS_WIDGET_DESKTOP_AURA_X11_DESKTOP_HANDLER_H_
 #define UI_VIEWS_WIDGET_DESKTOP_AURA_X11_DESKTOP_HANDLER_H_
 
 #include <X11/Xlib.h>
 // Get rid of a macro from Xlib.h that conflicts with Aura's RootWindow class.
 #undef RootWindow
@@ skipping 83 matching lines @@
   ::Window current_window_;
 
   // Whether we should treat |current_window_| as active. In particular, we
   // pretend that a window is deactivated after a call to DeactivateWindow().
   ActiveState current_window_active_state_;
 
   ui::X11AtomCache atom_cache_;
 
   bool wm_supports_active_window_;
 
+  XID modal_dialog_xid_;
+
   DISALLOW_COPY_AND_ASSIGN(X11DesktopHandler);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_WIDGET_DESKTOP_AURA_X11_DESKTOP_HANDLER_H_