Make File-Picker modal on Linux

ui/views/widget/desktop_aura/x11_desktop_handler.cc

Index: ui/views/widget/desktop_aura/x11_desktop_handler.cc
diff --git a/ui/views/widget/desktop_aura/x11_desktop_handler.cc b/ui/views/widget/desktop_aura/x11_desktop_handler.cc
index b7ca334936c924ce4cfac5ed073e300c0c6779ae..250b727a53b64737c84cb610791e72a47accfe55 100644
--- a/ui/views/widget/desktop_aura/x11_desktop_handler.cc
+++ b/ui/views/widget/desktop_aura/x11_desktop_handler.cc
@@ -170,6 +170,15 @@ uint32_t X11DesktopHandler::DispatchEvent(const ui::PlatformEvent& event) {
         ::Window window;
         if (ui::GetXIDProperty(x_root_window_, "_NET_ACTIVE_WINDOW", &window) &&
             window) {
+          // Set focus to the modal dialog instead of the host window.
+          DesktopWindowTreeHostX11* new_host =
+              views::DesktopWindowTreeHostX11::GetHostForXID(window);
+          if (new_host && new_host->GetModalDialog()) {
+            XSetInputFocus(xdisplay_, new_host->GetModalDialog(),
+                RevertToParent, CurrentTime);
+            break;
+          }
+
           OnActiveWindowChanged(window, ACTIVE);
         }
       }