Reduced number of UpdateDeviceList calls

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/Xatom.h>
 #include <X11/XKBlib.h>
 #include <X11/Xlib.h>
 
@@ skipping 191 matching lines @@
       last_seen_server_time_ = event_time;
   }
   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_HierarchyChanged) {
     UpdateDeviceList();
     hotplug_event_handler_->OnHotplugEvent();
   }
 
+  if (xevent->type == GenericEvent &&
+      xevent->xgeneric.evtype == XI_DeviceChanged) {
+    XIDeviceChangedEvent* xev =
+        static_cast<XIDeviceChangedEvent*>(xevent->xcookie.data);
+    if (xev->reason == XIDeviceChange) {
+      UpdateDeviceList();
+      hotplug_event_handler_->OnHotplugEvent();
+    } else {  // XISlaveSwitch
+      ui::DeviceDataManagerX11::GetInstance()->InvalidateScrollClasses();
+    }
+  }
+

[sadrul, 2016/06/20 19:37:30]

How about:

  bool should_update_list = false;
  if (xevent->type == GenericEvent) {
    if (xevent->xgeneric.evtype == XI_HierarchyChanged) {
      should_update_list = true;
    } else if (XI_DeviceChanged) {
      if (XIDeviceChange) {
        should_update_list = true;
      } else {
        DCHECK_EQ(XISlaveSwitch, xev->reason);
        InvalidateScrollClasses();
      }
    }
  }
  if (should_update_list) {
    UpdateDeviceList();
    hotplug...
  }

[Will Shackleton, 2016/06/21 16:27:46]

Done.

   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