Giving focus to an app shim brings windows belonging to that app to the foreground.

apps/app_shim/app_shim_host_mac.h

 // 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.
 
 #ifndef CHROME_BROWSER_WEB_APPLICATIONS_APP_SHIM_HOST_MAC_H_
 #define CHROME_BROWSER_WEB_APPLICATIONS_APP_SHIM_HOST_MAC_H_
 
 #include <string>
 
 #include "base/memory/scoped_ptr.h"
@@ skipping 42 matching lines @@
   // IPC::Sender implementation.
   virtual bool Send(IPC::Message* message) OVERRIDE;
 
  private:
   // The app shim process is requesting that an app be launched. Once it has
   // done so the |profile| and |app_id| are stored, and all future messages
   // from the app shim relate to the app it launched. It is an error for the
   // app shim to send multiple launch messages.
   void OnLaunchApp(std::string profile, std::string app_id);
 
+  // Called when the app shim process notifies that the app should be brought
+  // to the front (i.e. the user has clicked on the app's icon in the dock or
+  // Cmd+Tabbed to it.)
+  void OnFocus();
+
   bool LaunchAppImpl(const std::string& profile_dir, const std::string& app_id);
 
   // The AppShimHost listens to the NOTIFICATION_EXTENSION_HOST_DESTROYED
   // message to detect when the app closes. When that happens, the AppShimHost
   // closes the channel, which causes the app shim process to quit.
   virtual void Observe(int type,
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
   // Closes the channel and destroys the AppShimHost.
   void Close();
 
   scoped_ptr<IPC::ChannelProxy> channel_;
   std::string app_id_;
   Profile* profile_;
   content::NotificationRegistrar registrar_;
 };
 
 #endif  // CHROME_BROWSER_WEB_APPLICATIONS_APP_SHIM_HOST_MAC_H_