Fix Up SingletonHwnd Observer Lifetime Issues

content/browser/time_zone_monitor_win.cc

 // Copyright 2014 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 "content/browser/time_zone_monitor.h"
 
 #include <windows.h>
 
 #include "base/basictypes.h"
-#include "ui/gfx/win/singleton_hwnd.h"
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "base/memory/scoped_ptr.h"
+#include "ui/gfx/win/singleton_hwnd_observer.h"
 
 namespace content {
 
-class TimeZoneMonitorWin : public TimeZoneMonitor,
-                           public gfx::SingletonHwnd::Observer {
+class TimeZoneMonitorWin : public TimeZoneMonitor {
  public:
-  TimeZoneMonitorWin() : TimeZoneMonitor() {
-    gfx::SingletonHwnd::GetInstance()->AddObserver(this);
-  }
+  TimeZoneMonitorWin()
+      : TimeZoneMonitor(),
+        singleton_hwnd_observer_(
+            new gfx::SingletonHwndObserver(base::Bind(
+                &TimeZoneMonitorWin::OnTimeChange, base::Unretained(this)))) {}

[sky, 2015/04/28 13:20:34]

In general, unretained is error prone and it's best to document why it's safe.

[robliao, 2015/04/28 14:11:55]

See prior comment about this. 

 
-  virtual ~TimeZoneMonitorWin() {
-    gfx::SingletonHwnd::GetInstance()->RemoveObserver(this);
-  }
+  virtual ~TimeZoneMonitorWin() {}
 
-  // gfx::SingletonHwnd::Observer implementation.
-  virtual void OnWndProc(HWND hwnd,
-                         UINT message,
-                         WPARAM wparam,
-                         LPARAM lparam) override {
+ private:
+  void OnTimeChange(HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam) {
     if (message != WM_TIMECHANGE) {
       return;
     }
 
     NotifyRenderers();
   }
 
- private:
+  scoped_ptr<gfx::SingletonHwndObserver> singleton_hwnd_observer_;
+
   DISALLOW_COPY_AND_ASSIGN(TimeZoneMonitorWin);
 };
 
 // static
 scoped_ptr<TimeZoneMonitor> TimeZoneMonitor::Create() {
   return scoped_ptr<TimeZoneMonitor>(new TimeZoneMonitorWin());
 }
 
 }  // namespace content