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

chrome/app/chrome_main_app_mode_mac.mm

 // 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.
 
 // On Mac, one can't make shortcuts with command-line arguments. Instead, we
 // produce small app bundles which locate the Chromium framework and load it,
 // passing the appropriate data. This is the entry point into the framework for
 // those app bundles.
 
 #import <Cocoa/Cocoa.h>
@@ skipping 33 matching lines @@
 
  private:
   // IPC::Listener implemetation.
   virtual bool OnMessageReceived(const IPC::Message& message) OVERRIDE;
   virtual void OnChannelError() OVERRIDE;
 
   // If Chrome failed to launch the app, |success| will be false and the app
   // shim process should die.
   void OnLaunchAppDone(bool success);
 
+  // Called when the app is activated, either by the user clicking on it in the
+  // dock or by Cmd+Tabbing to it.
+  void OnDidActivateApplication();
+
   // Quits the app shim process.
   void Quit();
 
   IPC::ChannelProxy* channel_;
 
   DISALLOW_COPY_AND_ASSIGN(AppShimController);
 };
 
 AppShimController::AppShimController() : channel_(NULL) {
 }
@@ skipping 24 matching lines @@
 
   return handled;
 }
 
 void AppShimController::OnChannelError() {
   LOG(ERROR) << "App shim channel error.";
   Quit();
 }
 
 void AppShimController::OnLaunchAppDone(bool success) {
-  if (!success)
+  if (!success) {
     Quit();
+    return;
+  }
+  [[[NSWorkspace sharedWorkspace] notificationCenter]
+      addObserverForName:NSWorkspaceDidActivateApplicationNotification
+                  object:nil
+                   queue:nil
+              usingBlock:^(NSNotification* notification) {
+      NSRunningApplication* activated_app =
+          [[notification userInfo] objectForKey:NSWorkspaceApplicationKey];
+      if ([activated_app isEqual:[NSRunningApplication currentApplication]])
+        OnDidActivateApplication();
+  }];
 }
 
 void AppShimController::Quit() {
   [NSApp terminate:nil];
 }
 
+void AppShimController::OnDidActivateApplication() {
+  channel_->Send(new AppShimHostMsg_FocusApp);
+}
+
 //-----------------------------------------------------------------------------
 
 // A ReplyEventHandler is a helper class to send an Apple Event to a process
 // and call a callback when the reply returns.
 //
 // This is used to 'ping' the main Chrome process -- once Chrome has sent back
 // an Apple Event reply, it's guaranteed that it has opened the IPC channel
 // that the app shim will connect to.
 @interface ReplyEventHandler : NSObject {
   base::Callback<void(bool)> onReply_;
@@ skipping 171 matching lines @@
   // fully initialized don't receive a reply until its run loop starts. Once
   // the reply is received, Chrome will have opened its IPC port, guaranteed.
   [ReplyEventHandler pingProcess:psn andCall:base::Bind(&OnPingChromeReply)];
 
   MessageLoopForUI main_message_loop;
   main_message_loop.set_thread_name("MainThread");
   base::PlatformThread::SetName("CrAppShimMain");
   main_message_loop.Run();
   return 0;
 }