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 59 matching lines @@
   EnumDisplayMonitors(NULL, NULL, EnumMonitorCallback,
                       reinterpret_cast<LPARAM>(&displays));
   return displays;
 }
 
 }  // namespace
 
 namespace gfx {
 
 ScreenWin::ScreenWin()
-    : displays_(GetDisplays()) {
-  SingletonHwnd::GetInstance()->AddObserver(this);
-}
+    : displays_(GetDisplays()),
+      singleton_hwnd_observer_(new SingletonHwndObserver(
+          base::Bind(&ScreenWin::OnWndProc, 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 88 matching lines @@
   NOTREACHED();
   return NULL;
 }
 
 NativeWindow ScreenWin::GetNativeWindowFromHWND(HWND hwnd) const {
   NOTREACHED();
   return NULL;
 }
 
 }  // namespace gfx