Add PanelBrowserTitlebarGtk for panels on GTK.

chrome/browser/ui/panels/panel_browser_titlebar_gtk.cc

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/ui/panels/panel_browser_titlebar_gtk.h"
+
+PanelBrowserTitlebarGtk::PanelBrowserTitlebarGtk(
+    BrowserWindowGtk* browser_window, GtkWindow* window)
+    : BrowserTitlebar(browser_window, window) {
+
+}
+
+PanelBrowserTitlebarGtk::~PanelBrowserTitlebarGtk() {
+}
+
+bool PanelBrowserTitlebarGtk::BuildButton(const std::string& button_token,
+                                          bool left_side) {
+  // Panel only shows close button.
+  if (button_token != "close")
+    return false;
+
+  return BrowserTitlebar::BuildButton(button_token, left_side);
+}
+
+void PanelBrowserTitlebarGtk::ShowFaviconMenu(GdkEventButton* event) {
+  // Favicon menu is not supported in panels.
+}