Fix Up SingletonHwnd Observer Lifetime Issues

ui/gfx/screen_win.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/screen_win.h"
 
 #include <windows.h>
 
+#include "base/bind.h"
+#include "base/bind_helpers.h"
 #include "base/hash.h"
 #include "base/logging.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/win/win_util.h"
 #include "ui/gfx/display.h"
 #include "ui/gfx/win/dpi.h"
 
 namespace {
 
 MONITORINFOEX GetMonitorInfoForMonitor(HMONITOR monitor) {
@@ skipping 60 matching lines @@
                       reinterpret_cast<LPARAM>(&displays));
   return displays;
 }
 
 }  // namespace
 
 namespace gfx {
 
 ScreenWin::ScreenWin()
     : displays_(GetDisplays()) {
-  SingletonHwnd::GetInstance()->AddObserver(this);
+  singletonHwndObserver_.SetWndProc(
+      base::Bind(&ScreenWin::OnDisplayChange, base::Unretained(this)));
 }
 
-ScreenWin::~ScreenWin() {
-  SingletonHwnd::GetInstance()->RemoveObserver(this);
-}
+ScreenWin::~ScreenWin() {}
 
 gfx::Point ScreenWin::GetCursorScreenPoint() {
   POINT pt;
   GetCursorPos(&pt);
   gfx::Point cursor_pos_pixels(pt);
   return gfx::win::ScreenToDIPPoint(cursor_pos_pixels);
 }
 
 gfx::NativeWindow ScreenWin::GetWindowUnderCursor() {
   POINT cursor_loc;
@@ skipping 64 matching lines @@
 }
 
 void ScreenWin::AddObserver(DisplayObserver* observer) {
   change_notifier_.AddObserver(observer);
 }
 
 void ScreenWin::RemoveObserver(DisplayObserver* observer) {
   change_notifier_.RemoveObserver(observer);
 }
 
-void ScreenWin::OnWndProc(HWND hwnd,
-                          UINT message,
-                          WPARAM wparam,
-                          LPARAM lparam) {
+void ScreenWin::OnDisplayChange(HWND hwnd,
+                                UINT message,
+                                WPARAM wparam,
+                                LPARAM lparam) {
   if (message != WM_DISPLAYCHANGE)
     return;
 
   std::vector<gfx::Display> old_displays = displays_;
   displays_ = GetDisplays();
 
   change_notifier_.NotifyDisplaysChanged(old_displays, displays_);
 }
 
 HWND ScreenWin::GetHWNDFromNativeView(NativeView window) const {
   NOTREACHED();
   return NULL;
 }
 
 NativeWindow ScreenWin::GetNativeWindowFromHWND(HWND hwnd) const {
   NOTREACHED();
   return NULL;
 }
 
 }  // namespace gfx