Make panels not show on top when there is an app running in full screen mode.

chrome/browser/ui/panels/panel_browser_window_gtk.cc

Index: chrome/browser/ui/panels/panel_browser_window_gtk.cc
diff --git a/chrome/browser/ui/panels/panel_browser_window_gtk.cc b/chrome/browser/ui/panels/panel_browser_window_gtk.cc
index 3be8e961457d10949c4b7b091d3dbe61f188524b..d628e3478ed3d2f3d3b40e9d611410af30ec06a4 100644
--- a/chrome/browser/ui/panels/panel_browser_window_gtk.cc
+++ b/chrome/browser/ui/panels/panel_browser_window_gtk.cc
@@ -366,6 +366,11 @@ bool PanelBrowserWindowGtk::PreHandlePanelKeyboardEvent(
   return PreHandleKeyboardEvent(event, is_keyboard_shortcut);
 }
 
+void PanelBrowserWindowGtk::FullScreenModeChanged(bool is_full_screen) {
+  // Nothing to do here as z-order rules for panels ensures that they're below
+  // any app running in full screen mode.
+}
+
 void PanelBrowserWindowGtk::HandlePanelKeyboardEvent(
     const NativeWebKeyboardEvent& event) {
   HandleKeyboardEvent(event);