Add PanelBrowserTitlebarGtk for panels on GTK.

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 4d3a32446357d6f6174ecdac21878779c8ab89df..b3363beb6ac7a2bb120852252e815bf5c4a1e7d4 100644
--- a/chrome/browser/ui/panels/panel_browser_window_gtk.cc
+++ b/chrome/browser/ui/panels/panel_browser_window_gtk.cc
@@ -9,6 +9,7 @@
 #include "chrome/browser/ui/gtk/browser_titlebar.h"
 #include "chrome/browser/ui/panels/panel.h"
 #include "chrome/browser/ui/panels/panel_bounds_animation.h"
+#include "chrome/browser/ui/panels/panel_browser_titlebar_gtk.h"
 #include "chrome/browser/ui/panels/panel_drag_gtk.h"
 #include "chrome/browser/ui/panels/panel_manager.h"
 #include "chrome/browser/ui/panels/panel_strip.h"
@@ -90,6 +91,10 @@ void PanelBrowserWindowGtk::Init() {
       content::Source<GtkWindow>(window()));
 }
 
+BrowserTitlebar* PanelBrowserWindowGtk::CreateBrowserTitlebar() {
+  return new PanelBrowserTitlebarGtk(this, window());
+}
+
 bool PanelBrowserWindowGtk::GetWindowEdge(int x, int y, GdkWindowEdge* edge) {
   // Only detect the window edge when panels can be resized by the user.
   // This method is used by the base class to detect when the cursor has