Gtk3 ui: Add libgtk3ui as a separate build component

chrome/browser/ui/libgtk2ui/gtk2_event_loop.h

-// Copyright 2014 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.
-
-#ifndef CHROME_BROWSER_UI_LIBGTK2UI_GTK2_EVENT_LOOP_H_
-#define CHROME_BROWSER_UI_LIBGTK2UI_GTK2_EVENT_LOOP_H_
-
-#include "base/macros.h"
-#include "ui/base/glib/glib_integers.h"
-
-typedef union _GdkEvent GdkEvent;
-typedef struct _GdkEventKey GdkEventKey;
-
-namespace base {
-template<typename Type> struct DefaultSingletonTraits;
-}
-
-namespace libgtk2ui {
-
-class Gtk2EventLoop {
- public:
-  static Gtk2EventLoop* GetInstance();
-
- private:
-  friend struct base::DefaultSingletonTraits<Gtk2EventLoop>;
-
-  Gtk2EventLoop();
-  ~Gtk2EventLoop();
-
-  static void DispatchGdkEvent(GdkEvent* gdk_event, gpointer);
-  static void ProcessGdkEventKey(const GdkEventKey& gdk_event_key);
-
-  DISALLOW_COPY_AND_ASSIGN(Gtk2EventLoop);
-};
-
-}  // namespace libgtk2ui
-
-#endif  // CHROME_BROWSER_UI_LIBGTK2UI_GTK2_EVENT_LOOP_H_