Add PanelBrowserTitlebarGtk for panels on GTK.

chrome/browser/ui/gtk/browser_window_gtk.cc

Index: chrome/browser/ui/gtk/browser_window_gtk.cc
diff --git a/chrome/browser/ui/gtk/browser_window_gtk.cc b/chrome/browser/ui/gtk/browser_window_gtk.cc
index 2d37e6903e0a6ca2e6dd59f92b17fa832a3bd105..773cbf5d045e8665c794b7cad75dc0fa41202890 100644
--- a/chrome/browser/ui/gtk/browser_window_gtk.cc
+++ b/chrome/browser/ui/gtk/browser_window_gtk.cc
@@ -1819,7 +1819,7 @@ void BrowserWindowGtk::InitWidgets() {
   tabstrip_->Init();
 
   // Build the titlebar (tabstrip + header space + min/max/close buttons).
-  titlebar_.reset(new BrowserTitlebar(this, window_));
+  titlebar_.reset(CreateBrowserTitlebar());
 
   // Insert the tabstrip into the window.
   gtk_box_pack_start(GTK_BOX(window_vbox_), titlebar_->widget(), FALSE, FALSE,
@@ -2454,6 +2454,10 @@ bool BrowserWindowGtk::UsingCustomPopupFrame() const {
          (browser()->is_type_popup() || browser()->is_type_panel());
 }
 
+BrowserTitlebar* BrowserWindowGtk::CreateBrowserTitlebar() {
+  return new BrowserTitlebar(this, window_);
+}
+
 bool BrowserWindowGtk::GetWindowEdge(int x, int y, GdkWindowEdge* edge) {
   if (!UseCustomFrame())
     return false;