Partial revert of https://codereview.chromium.org/1911973002/

ui/gfx/win/singleton_hwnd.cc

 // 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.
 
 #include "ui/gfx/win/singleton_hwnd.h"
 
 #include "base/memory/singleton.h"
 #include "base/message_loop/message_loop.h"
 #include "ui/gfx/win/singleton_hwnd_observer.h"
 
@@ skipping 13 matching lines @@
   FOR_EACH_OBSERVER(SingletonHwndObserver,
                     observer_list_,
                     OnWndProc(window, message, wparam, lparam));
   return false;
 }
 
 SingletonHwnd::SingletonHwnd() {
   if (!base::MessageLoopForUI::IsCurrent()) {
     // Creating this window in (e.g.) a renderer inhibits shutdown on
     // Windows. See http://crbug.com/230122 and http://crbug.com/236039.
+    LOG(FATAL) << "Cannot create windows on non-UI thread!";
     return;
   }
   WindowImpl::Init(NULL, Rect());
 }
 
 SingletonHwnd::~SingletonHwnd() {
   // WindowImpl will clean up the hwnd value on WM_NCDESTROY.
   if (hwnd())
     DestroyWindow(hwnd());
 
   // Tell all of our current observers to clean themselves up.
   FOR_EACH_OBSERVER(SingletonHwndObserver, observer_list_, ClearWndProc());
 }
 
 void SingletonHwnd::AddObserver(SingletonHwndObserver* observer) {
   observer_list_.AddObserver(observer);
 }
 
 void SingletonHwnd::RemoveObserver(SingletonHwndObserver* observer) {
   observer_list_.RemoveObserver(observer);
 }
 
 }  // namespace gfx