With the recent change to the ExternalTabContainer to have it subclass Widget...

chrome/browser/external_tab_container.cc

 // Copyright (c) 2006-2008 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 "chrome/browser/external_tab_container.h"
 
 #include "app/win_util.h"
 #include "base/logging.h"
 #include "base/win_util.h"
 #include "chrome/browser/automation/automation_provider.h"
@@ skipping 106 matching lines @@
 void ExternalTabContainer::SetInitialFocus(bool reverse) {
   DCHECK(tab_contents_);
   if (tab_contents_) {
     static_cast<TabContents*>(tab_contents_)->Focus();
     static_cast<TabContents*>(tab_contents_)->SetInitialFocus(reverse);
   }
 }
 
 // static
 bool ExternalTabContainer::IsExternalTabContainer(HWND window) {
-  std::wstring class_name = win_util::GetClassName(window);
-  return _wcsicmp(class_name.c_str(), chrome::kExternalTabWindowClass) == 0;
+  if (GetProp(window, kWindowObjectKey) != NULL)
+    return true;
+  
+  return false;
 }
 
 // static
 ExternalTabContainer* ExternalTabContainer::GetContainerForTab(
     HWND tab_window) {
   HWND parent_window = ::GetParent(tab_window);
   if (!::IsWindow(parent_window)) {
     return NULL;
   }
   if (!IsExternalTabContainer(parent_window)) {
@@ skipping 244 matching lines @@
     NotificationService::current()->Notify(
         NotificationType::EXTERNAL_TAB_CLOSED,
         Source<NavigationController>(&tab_contents_->controller()),
         Details<ExternalTabContainer>(this));
 
     delete tab_contents_;
     tab_contents_ = NULL;
   }
 }