Swap main menu with app-specific menu when app window focused.

chrome/browser/ui/cocoa/extensions/native_app_window_cocoa.mm

Index: chrome/browser/ui/cocoa/extensions/native_app_window_cocoa.mm
diff --git a/chrome/browser/ui/cocoa/extensions/native_app_window_cocoa.mm b/chrome/browser/ui/cocoa/extensions/native_app_window_cocoa.mm
index 583f7e95dc72ca8526e8fc80f571330c84e4e440..422bc1d67a56be9daf282f51c50120bbf1584fdf 100644
--- a/chrome/browser/ui/cocoa/extensions/native_app_window_cocoa.mm
+++ b/chrome/browser/ui/cocoa/extensions/native_app_window_cocoa.mm
@@ -6,6 +6,7 @@
 
 #include "base/mac/mac_util.h"
 #include "base/strings/sys_string_conversions.h"
+#include "chrome/browser/app_controller_mac.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/cocoa/browser_window_utils.h"
 #import "chrome/browser/ui/cocoa/chrome_event_processing_window.h"
@@ -745,6 +746,9 @@ void NativeAppWindowCocoa::WindowDidBecomeKey() {
       web_contents()->GetRenderWidgetHostView();
   if (rwhv)
     rwhv->SetActive(true);
+  const extensions::Extension* app = shell_window_->extension();
+  [[NSApp delegate] setMenuBarToApp:base::SysUTF8ToNSString(app->id())
+                          withTitle:base::SysUTF8ToNSString(app->name())];
   shell_window_->OnNativeWindowActivated();
 }