Add Hide to app menu.

apps/app_shim/app_shim_host_mac.cc

 // Copyright 2013 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 "apps/app_shim/app_shim_host_mac.h"
 
 #include "apps/app_shim/app_shim_handler_mac.h"
 #include "apps/app_shim/app_shim_messages.h"
 #include "base/bind.h"
 #include "base/files/file_path.h"
@@ skipping 96 matching lines @@
   if (!initial_launch_finished_) {
     Send(new AppShimMsg_LaunchApp_Done(result));
     initial_launch_finished_ = true;
   }
 }
 
 void AppShimHost::OnAppClosed() {
   Close();
 }
 
+void AppShimHost::OnAppHide() {
+  Send(new AppShimMsg_Hide);
+}
+
 void AppShimHost::OnAppRequestUserAttention() {
   Send(new AppShimMsg_RequestUserAttention);
 }
 
 void AppShimHost::Close() {
   DCHECK(CalledOnValidThread());
   delete this;
 }