Change SingletonHwnd to be based on WindowImpl.

ui/base/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/base/win/singleton_hwnd.h"
 
 #include "base/memory/singleton.h"
-#include "base/process_util.h"
-#include "base/win/wrapped_window_proc.h"
-#include "ui/base/win/hwnd_util.h"
-
-namespace {
-
-// Windows class name to use for the listener window.
-const wchar_t kWindowClassName[] = L"Chrome_SingletonHwnd";
-
-// Windows callback for listening for WM_* messages.
-LRESULT CALLBACK ListenerWindowProc(HWND hwnd,
-                                    UINT message,
-                                    WPARAM wparam,
-                                    LPARAM lparam) {
-  ui::SingletonHwnd::GetInstance()->OnWndProc(hwnd, message, wparam, lparam);
-  return ::DefWindowProc(hwnd, message, wparam, lparam);
-}
-
-// Creates a listener window to receive WM_* messages.
-HWND CreateListenerWindow() {
-  WNDCLASSEX wc = {0};
-  wc.cbSize = sizeof(wc);
-  wc.lpfnWndProc = base::win::WrappedWindowProc<ListenerWindowProc>;
-  wc.hInstance = base::GetModuleFromAddress(&ListenerWindowProc);
-  wc.lpszClassName = kWindowClassName;
-  ATOM window_class = ::RegisterClassEx(&wc);
-  DCHECK(window_class);
-
-  return ::CreateWindow(MAKEINTATOM(window_class), 0, 0, 0, 0, 0, 0, 0, 0,
-                        wc.hInstance, 0);
-}
-
-}  // namespace
 
 namespace ui {
 
 // static
 SingletonHwnd* SingletonHwnd::GetInstance() {
   return Singleton<SingletonHwnd>::get();
 }
 
 void SingletonHwnd::AddObserver(Observer* observer) {
-  if (!listener_window_) {
-    listener_window_ = CreateListenerWindow();
-    ui::CheckWindowCreated(listener_window_);
-  }
+  if (!hwnd())
+    WindowImpl::Init(NULL, gfx::Rect());
   observer_list_.AddObserver(observer);
 }
 
 void SingletonHwnd::RemoveObserver(Observer* observer) {
   observer_list_.RemoveObserver(observer);
 }
 
-void SingletonHwnd::OnWndProc(HWND hwnd,
-                              UINT message,
-                              WPARAM wparam,
-                              LPARAM lparam) {
+BOOL SingletonHwnd::ProcessWindowMessage(HWND window,
+                                         UINT message,
+                                         WPARAM wparam,
+                                         LPARAM lparam,
+                                         LRESULT& result,
+                                         DWORD msg_map_id) {
   FOR_EACH_OBSERVER(Observer,
                     observer_list_,
-                    OnWndProc(hwnd, message, wparam, lparam));
+                    OnWndProc(window, message, wparam, lparam));
+  result = ::DefWindowProc(window, message, wparam, lparam);

[msw, 2012/04/02 22:51:03]

Can you return false here without explicitly calling DefWindowProc?

DefWindowProc can potentially open up a can of worms. There's no visible window
here to experience visible artifacts like NativeWidgetWin, but you might face
re-entrance and potentially wonky behavior by Windows.

+  return true;
 }
 
-SingletonHwnd::SingletonHwnd()
-    : listener_window_(NULL) {
+SingletonHwnd::SingletonHwnd() {
 }
 
 SingletonHwnd::~SingletonHwnd() {
-  if (listener_window_) {
-    ::DestroyWindow(listener_window_);
-    ::UnregisterClass(kWindowClassName, GetModuleHandle(NULL));
-  }
 }
 
 }  // namespace ui