Fix Up SingletonHwnd Observer Lifetime Issues

ui/gfx/screen_win.cc

Index: ui/gfx/screen_win.cc
diff --git a/ui/gfx/screen_win.cc b/ui/gfx/screen_win.cc
index 9210971d7b45d63865c6de2dd1dc0f2a9c75d7e1..91e8d24bc42f7a16070296237e26a7d05f830258 100644
--- a/ui/gfx/screen_win.cc
+++ b/ui/gfx/screen_win.cc
@@ -6,6 +6,8 @@
 
 #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"
@@ -86,12 +88,11 @@ 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;
@@ -176,10 +177,10 @@ 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;