Adding GetEventSource() method to the WindowTreeHost class.

ui/views/widget/desktop_aura/desktop_window_tree_host_x11.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 "ui/views/widget/desktop_aura/desktop_window_tree_host_x11.h"
 
 #include <X11/extensions/shape.h>
 #include <X11/extensions/XInput2.h>
 #include <X11/Xatom.h>
 #include <X11/Xregion.h>
@@ skipping 747 matching lines @@
   }
 }
 
 bool DesktopWindowTreeHostX11::IsAnimatingClosed() const {
   return false;
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // DesktopWindowTreeHostX11, aura::WindowTreeHost implementation:
 
+ui::EventSource* DesktopWindowTreeHostX11::GetEventSource() {
+  return this;
+}
+
 gfx::AcceleratedWidget DesktopWindowTreeHostX11::GetAcceleratedWidget() {
   return xwindow_;
 }
 
 void DesktopWindowTreeHostX11::Show() {
   ShowWindowWithState(ui::SHOW_STATE_NORMAL);
   native_widget_delegate_->OnNativeWidgetVisibilityChanged(true);
 }
 
 void DesktopWindowTreeHostX11::Hide() {
@@ skipping 856 matching lines @@
   if (linux_ui) {
     ui::NativeTheme* native_theme = linux_ui->GetNativeTheme();
     if (native_theme)
       return native_theme;
   }
 
   return ui::NativeTheme::instance();
 }
 
 }  // namespace views