Fixed first step of scrolling not applying

ui/events/platform/x11/x11_event_source.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.h"
 
 #include <X11/XKBlib.h>
 #include <X11/Xlib.h>
 
 #include "base/logging.h"
@@ skipping 93 matching lines @@
   }
   delegate_->ProcessXEvent(xevent);
   PostDispatchEvent(xevent);
   if (have_cookie)
     XFreeEventData(xevent->xgeneric.display, &xevent->xcookie);
 }
 
 void X11EventSource::PostDispatchEvent(XEvent* xevent) {
   if (xevent->type == GenericEvent &&
       (xevent->xgeneric.evtype == XI_HierarchyChanged ||
-       xevent->xgeneric.evtype == XI_DeviceChanged)) {
+       (xevent->xgeneric.evtype == XI_DeviceChanged &&
+        static_cast<XIDeviceChangedEvent*>(xevent->xcookie.data)->reason ==
+            XIDeviceChange))) {
     ui::UpdateDeviceList();
     hotplug_event_handler_->OnHotplugEvent();
   }
 
   if (xevent->type == EnterNotify &&
       xevent->xcrossing.detail != NotifyInferior &&
       xevent->xcrossing.mode != NotifyUngrab) {
     // Clear stored scroll data
     ui::DeviceDataManagerX11::GetInstance()->InvalidateScrollClasses();
   }
 }
 
 void X11EventSource::StopCurrentEventStream() {
   continue_stream_ = false;
 }
 
 void X11EventSource::OnDispatcherListChanged() {
   if (!hotplug_event_handler_) {
     hotplug_event_handler_.reset(new X11HotplugEventHandler());
     // Force the initial device query to have an update list of active devices.
     hotplug_event_handler_->OnHotplugEvent();
   }
 }
 
 }  // namespace ui