Ensure Windows window classes are unregistered on shutdown (take 2)

chrome/browser/process_singleton_win.cc

Index: chrome/browser/process_singleton_win.cc
===================================================================
--- chrome/browser/process_singleton_win.cc	(revision 14503)
+++ chrome/browser/process_singleton_win.cc	(working copy)
@@ -45,8 +45,10 @@
 }
 
 ProcessSingleton::~ProcessSingleton() {
-  if (window_)
+  if (window_) {
     DestroyWindow(window_);
+    UnregisterClass(chrome::kMessageWindowClass, GetModuleHandle(NULL));
+  }
 }
 
 bool ProcessSingleton::NotifyOtherProcess() {
@@ -142,7 +144,8 @@
   wc.lpfnWndProc = ProcessSingleton::WndProcStatic;
   wc.hInstance = hinst;
   wc.lpszClassName = chrome::kMessageWindowClass;
-  RegisterClassEx(&wc);
+  ATOM clazz = RegisterClassEx(&wc);
+  DCHECK(clazz);
 
   std::wstring user_data_dir;
   PathService::Get(chrome::DIR_USER_DATA, &user_data_dir);