base: Stop passing a non-const ref to ObserverListBase::Iterator.

ui/aura/window.cc

Index: ui/aura/window.cc
diff --git a/ui/aura/window.cc b/ui/aura/window.cc
index ab1a2da85fca8ff6911f10333006355627a5c03e..3fe502797e0ccf5d30fda8393f2b91c4d6605f63 100644
--- a/ui/aura/window.cc
+++ b/ui/aura/window.cc
@@ -262,7 +262,7 @@ Window::~Window() {
 
   if (delegate_)
     delegate_->OnWindowDestroyed(this);
-  ObserverListBase<WindowObserver>::Iterator iter(observers_);
+  ObserverListBase<WindowObserver>::Iterator iter(&observers_);
   for (WindowObserver* observer = iter.GetNext(); observer;
        observer = iter.GetNext()) {
     RemoveObserver(observer);