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 5ab84f9928e6d0f6305ee1642d3c4bf18c9bdfb5..9b20295cc62fa621bbba890d0640e826f090c710 100644
--- a/ui/views/widget/desktop_aura/x11_desktop_handler.cc
+++ b/ui/views/widget/desktop_aura/x11_desktop_handler.cc
@@ -228,8 +228,15 @@ void X11DesktopHandler::OnActiveWindowChanged(::Window xid,
   if (active_state == ACTIVE) {
     DesktopWindowTreeHostX11* new_host =
         views::DesktopWindowTreeHostX11::GetHostForXID(xid);
-    if (new_host)
-      new_host->HandleNativeWidgetActivationChanged(true);
+    if (new_host) {
+      // Set focus to the modal dialog instead of the host window.
+      if (new_host->GetModalDialog()) {
+        XSetInputFocus(xdisplay_, new_host->GetModalDialog(),
+            RevertToParent, CurrentTime);
+      } else {
+        new_host->HandleNativeWidgetActivationChanged(true);
+      }
+    }
   }
 }