[Win] Battery Status API: use SingletonHwnd for notifications.

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..e3587a22d4871603b4b55537883f8f574ea25526 100644
--- a/ui/gfx/win/singleton_hwnd.cc
+++ b/ui/gfx/win/singleton_hwnd.cc
@@ -15,10 +15,12 @@ SingletonHwnd* SingletonHwnd::GetInstance() {
 }
 
 void SingletonHwnd::AddObserver(Observer* observer) {
+  DCHECK(thread_checker_.CalledOnValidThread());
   observer_list_.AddObserver(observer);
 }
 
 void SingletonHwnd::RemoveObserver(Observer* observer) {
+  DCHECK(thread_checker_.CalledOnValidThread());
   if (!hwnd())
     return;
   observer_list_.RemoveObserver(observer);
@@ -37,10 +39,11 @@ BOOL SingletonHwnd::ProcessWindowMessage(HWND window,
 }
 
 SingletonHwnd::SingletonHwnd() {
+  DCHECK(thread_checker_.CalledOnValidThread());
   if (!base::MessageLoopForUI::IsCurrent()) {
     // Creating this window in (e.g.) a renderer inhibits shutdown on
     // Windows. See http://crbug.com/230122 and http://crbug.com/236039.
-    DLOG(ERROR) << "Cannot create windows on non-UI thread!";
+    DLOG(FATAL) << "Cannot create windows on non-UI thread!";
     return;
   }
   WindowImpl::Init(NULL, Rect());