Fix Up SingletonHwnd Observer Lifetime Issues

ui/gfx/win/singleton_hwnd.cc

Index: ui/gfx/win/singleton_hwnd.cc
diff --git a/ui/gfx/win/singleton_hwnd.cc b/ui/gfx/win/singleton_hwnd.cc
index fc4d11f2d5e0d8146d9a3fa5c0f666e2e3c86676..79d51512545ea2b82211d54035e70624132328e5 100644
--- a/ui/gfx/win/singleton_hwnd.cc
+++ b/ui/gfx/win/singleton_hwnd.cc
@@ -6,6 +6,7 @@
 
 #include "base/memory/singleton.h"
 #include "base/message_loop/message_loop.h"
+#include "ui/gfx/win/singleton_hwnd_observer.h"
 
 namespace gfx {
 
@@ -14,23 +15,13 @@ SingletonHwnd* SingletonHwnd::GetInstance() {
   return Singleton<SingletonHwnd>::get();
 }
 
-void SingletonHwnd::AddObserver(Observer* observer) {
-  observer_list_.AddObserver(observer);
-}
-
-void SingletonHwnd::RemoveObserver(Observer* observer) {
-  if (!hwnd())
-    return;
-  observer_list_.RemoveObserver(observer);
-}
-
 BOOL SingletonHwnd::ProcessWindowMessage(HWND window,
                                          UINT message,
                                          WPARAM wparam,
                                          LPARAM lparam,
                                          LRESULT& result,
                                          DWORD msg_map_id) {
-  FOR_EACH_OBSERVER(Observer,
+  FOR_EACH_OBSERVER(SingletonHwndObserver,
                     observer_list_,
                     OnWndProc(window, message, wparam, lparam));
   return false;
@@ -47,6 +38,18 @@ SingletonHwnd::SingletonHwnd() {
 }
 
 SingletonHwnd::~SingletonHwnd() {
+  // WindowImpl will clean up the hwnd value on WM_NCDESTROY.
+  DestroyWindow(hwnd());
+  DCHECK(!observer_list_.might_have_observers());

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

Instead of this define observer_list_ like base::ObserverList<..., true>
observer_list_; and you'll get it for free.

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

Neat. Done.

+}
+
+void SingletonHwnd::AddObserver(SingletonHwndObserver* observer) {
+  DCHECK(hwnd());
+  observer_list_.AddObserver(observer);
+}
+
+void SingletonHwnd::RemoveObserver(SingletonHwndObserver* observer) {
+  observer_list_.RemoveObserver(observer);
 }
 
 }  // namespace gfx