Adding GetEventSource() method to the WindowTreeHost class.

ui/aura/window_tree_host_mac.mm

 // 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.
 
 #include <Cocoa/Cocoa.h>
 
 #include "ui/aura/window_tree_host_mac.h"
 #include "ui/aura/window_tree_host.h"
 
 namespace aura {
 
 WindowTreeHostMac::WindowTreeHostMac(const gfx::Rect& bounds) {
   window_.reset(
       [[NSWindow alloc]
           initWithContentRect:NSRectFromCGRect(bounds.ToCGRect())
                     styleMask:NSBorderlessWindowMask
                       backing:NSBackingStoreBuffered
                         defer:NO]);
   CreateCompositor(GetAcceleratedWidget());
 }
 
 WindowTreeHostMac::~WindowTreeHostMac() {
   DestroyDispatcher();
 }
 
+EventSource* WindowTreeHostMac::GetEventSource() {
+  NOTIMPLEMENTED();
+  return nil;
+}
+
 gfx::AcceleratedWidget WindowTreeHostMac::GetAcceleratedWidget() {
   return [window_ contentView];
 }
 void WindowTreeHostMac::Show() {
   [window_ makeKeyAndOrderFront:nil];
 }
 
 void WindowTreeHostMac::Hide() {
   [window_ orderOut:nil];
 }
@@ skipping 69 matching lines @@
   return new WindowTreeHostMac(bounds);
 }
 
 // static
 gfx::Size WindowTreeHost::GetNativeScreenSize() {
   NOTIMPLEMENTED();
   return gfx::Size(1024, 768);
 }
 
 }  // namespace aura