Split the singleton hwnd from screen_compatible_dc_win.cc.

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/bind.h"
+#include "base/callback.h"
+#include "base/logging.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"SingletonHwnd";

[cpu_(ooo_6.6-7.5), 2012/02/09 21:58:37]

too short. How about Chrome.SigletonHwnd or 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);

[cpu_(ooo_6.6-7.5), 2012/02/09 21:58:37]

hmm, kind of weird that you can get to act on the message but not set the return
value. A lot of useful actions require you to return a different value from what
DefWindowProc requires.

+}
+
+// Creates a listener window to receive WM_* messages.
+HWND CreateListenerWindow() {
+  HINSTANCE hinst = 0;
+  if (!::GetModuleHandleExA(GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS,
+                            reinterpret_cast<char*>(&ListenerWindowProc),
+                            &hinst)) {
+    NOTREACHED();
+  }
+
+  WNDCLASSEX wc = {0};
+  wc.cbSize = sizeof(wc);
+  wc.lpfnWndProc = base::win::WrappedWindowProc<ListenerWindowProc>;
+  wc.hInstance = hinst;
+  wc.lpszClassName = kWindowClassName;
+  ATOM clazz = ::RegisterClassEx(&wc);

[cpu_(ooo_6.6-7.5), 2012/02/09 21:58:37]

I can smell the copy and paste :) please use var names in english, like
window_class or win_class or whatever.

+  DCHECK(clazz);
+
+  return ::CreateWindow(MAKEINTATOM(clazz), 0, 0, 0, 0, 0, 0, HWND_MESSAGE, 0,
+                        hinst, 0);

[cpu_(ooo_6.6-7.5), 2012/02/09 21:58:37]

wait, this is also a message only window.. ??  you don't get broadcast messages.

+}
+
+}  // namespace
+
+namespace ui {
+
+// static
+SingletonHwnd* SingletonHwnd::GetInstance() {
+  return Singleton<SingletonHwnd>::get();
+}
+
+void SingletonHwnd::RegisterListener(WndProcCallback& callback) {
+  if (!listener_window_) {
+    listener_window_ = CreateListenerWindow();
+    ui::CheckWindowCreated(listener_window_);
+  }
+  listeners_.push_back(callback);
+}
+
+void SingletonHwnd::OnWndProc(HWND hwnd,
+                              UINT message,
+                              WPARAM wparam,
+                              LPARAM lparam) {
+  for (size_t i = 0; i < listeners_.size(); ++i)
+    listeners_[i].Run(hwnd, message, wparam, lparam);
+}
+
+SingletonHwnd::SingletonHwnd()
+    : listener_window_(NULL) {
+}
+
+SingletonHwnd::~SingletonHwnd() {
+  if (listener_window_) {
+    ::DestroyWindow(listener_window_);
+    ::UnregisterClass(kWindowClassName, GetModuleHandle(NULL));
+  }
+}
+
+}  // namespace ui