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

ui/events/platform/x11/x11_event_source_libevent.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 "ui/events/platform/x11/x11_event_source_libevent.h"
 
 #include <X11/Xlib.h>
 #include <X11/extensions/XInput2.h>
 
 #include <memory>
@@ skipping 161 matching lines @@
     return;
 
   int fd = ConnectionNumber(event_source_.display());
   base::MessageLoopForUI::current()->WatchFileDescriptor(
       fd, true, base::MessagePumpLibevent::WATCH_READ, &watcher_controller_,
       this);
   initialized_ = true;
 }
 
 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;
   }
 }
 
 void X11EventSourceLibevent::StopCurrentEventStream() {
   event_source_.StopCurrentEventStream();
 }
 
 void X11EventSourceLibevent::OnDispatcherListChanged() {
   AddEventWatcher();
   event_source_.OnDispatcherListChanged();
 }
 
 void X11EventSourceLibevent::OnFileCanReadWithoutBlocking(int fd) {
   event_source_.DispatchXEvents();
 }
 
 void X11EventSourceLibevent::OnFileCanWriteWithoutBlocking(int fd) {
   NOTREACHED();
 }
 
 }  // namespace ui