Allow to open multiple modal file-pickers in Linux

ui/views/widget/desktop_aura/desktop_window_tree_host_x11.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_DESKTOP_WINDOW_TREE_HOST_X11_H_
 #define UI_VIEWS_WIDGET_DESKTOP_AURA_DESKTOP_WINDOW_TREE_HOST_X11_H_
 
 #include <stddef.h>
 #include <stdint.h>
 #include <X11/extensions/shape.h>
@@ skipping 67 matching lines @@
   void RemoveObserver(DesktopWindowTreeHostObserverX11* observer);
 
   // Swaps the current handler for events in the non client view with |handler|.
   void SwapNonClientEventHandler(std::unique_ptr<ui::EventHandler> handler);
 
   // Runs the |func| callback for each content-window, and deallocates the
   // internal list of open windows.
   static void CleanUpWindowList(void (*func)(aura::Window* window));
 
   // Disables event listening to make |dialog| modal.
-  std::unique_ptr<base::Closure> DisableEventListening(XID dialog);
-
-  // Returns XID of dialog currently displayed. When it returns 0,
-  // there is no dialog on the host window.
-  XID GetModalDialog();
+  std::unique_ptr<base::Closure> DisableEventListening();
 
  protected:
   // Overridden from DesktopWindowTreeHost:
   void Init(aura::Window* content_window,
             const Widget::InitParams& params) override;
   void OnNativeWidgetCreated(const Widget::InitParams& params) override;
   void OnWidgetInitDone() override;
   void OnNativeWidgetActivationChanged(bool active) override;
   std::unique_ptr<corewm::Tooltip> CreateTooltip() override;
   std::unique_ptr<aura::client::DragDropClient> CreateDragDropClient(
@@ skipping 320 matching lines @@
   // Used for tracking activation state in {Before|After}ActivationStateChanged.
   bool was_active_;
   bool had_pointer_;
   bool had_pointer_grab_;
   bool had_window_focus_;
 
   base::CancelableCallback<void()> delayed_resize_task_;
 
   std::unique_ptr<aura::ScopedWindowTargeter> targeter_for_modal_;
 
-  XID modal_dialog_xid_;
+  uint32_t modal_dialog_counter_;
 
   base::WeakPtrFactory<DesktopWindowTreeHostX11> close_widget_factory_;
   base::WeakPtrFactory<DesktopWindowTreeHostX11> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DesktopWindowTreeHostX11);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_WIDGET_DESKTOP_AURA_DESKTOP_WINDOW_TREE_HOST_X11_H_