Remove usage of base::ObserverList<T>::Iter::GetNext() in //ui.

ui/events/platform/x11/x11_event_source_libevent.cc

Index: ui/events/platform/x11/x11_event_source_libevent.cc
diff --git a/ui/events/platform/x11/x11_event_source_libevent.cc b/ui/events/platform/x11/x11_event_source_libevent.cc
index 708ab4104a4d9dc4821b50414e1d6f094950805d..3d5863b4e83c725cb0f9261c514f2563840545f3 100644
--- a/ui/events/platform/x11/x11_event_source_libevent.cc
+++ b/ui/events/platform/x11/x11_event_source_libevent.cc
@@ -179,12 +179,9 @@ void X11EventSourceLibevent::AddEventWatcher() {
 }
 
 void X11EventSourceLibevent::DispatchXEventToXEventDispatchers(XEvent* xevent) {
-  if (dispatchers_xevent_.might_have_observers()) {

[sky, 2016/10/13 02:20:57]

This code is called on every mouse event, so it seems worth optimizing. Are you
sure you don't want the check here?

[dcheng, 2016/10/13 02:39:22]

Creation of the iterator is cheap if might_have_observers() is false. Ideally,
I'd like to remove this from ObserverList altogether.

[loyso (OOO), 2016/10/13 02:40:26]

We have that optimization as a built-in. If underlying vector is empty, begin()
and end() return lightweight empty iterators, not involving weak pointers
creation stuff.

-    base::ObserverList<XEventDispatcher>::Iterator iter(&dispatchers_xevent_);
-    while (XEventDispatcher* dispatcher = iter.GetNext()) {
-      if (dispatcher->DispatchXEvent(xevent))
-        break;
-    }
+  for (auto& dispatcher : dispatchers_xevent_) {
+    if (dispatcher.DispatchXEvent(xevent))
+      break;
   }
 }