Reduced number of UpdateDeviceList calls

ui/events/platform/x11/x11_event_source.cc

Index: ui/events/platform/x11/x11_event_source.cc
diff --git a/ui/events/platform/x11/x11_event_source.cc b/ui/events/platform/x11/x11_event_source.cc
index aa2549adc1ba8b64a6378a02d6d5eb1c05b77c08..a5795792f2a8a86a3becc9d434fc96bf22be31a2 100644
--- a/ui/events/platform/x11/x11_event_source.cc
+++ b/ui/events/platform/x11/x11_event_source.cc
@@ -208,9 +208,25 @@ void X11EventSource::ExtractCookieDataDispatchEvent(XEvent* xevent) {
 }
 
 void X11EventSource::PostDispatchEvent(XEvent* xevent) {
-  if (xevent->type == GenericEvent &&
-      (xevent->xgeneric.evtype == XI_HierarchyChanged ||
-       xevent->xgeneric.evtype == XI_DeviceChanged)) {
+  bool should_update_device_list = false;
+
+  if (xevent->type == GenericEvent) {
+    if (xevent->xgeneric.evtype == XI_HierarchyChanged) {
+      should_update_device_list = true;
+    } else if (xevent->xgeneric.evtype == XI_DeviceChanged) {
+      XIDeviceChangedEvent* xev =
+          static_cast<XIDeviceChangedEvent*>(xevent->xcookie.data);
+      if (xev->reason == XIDeviceChange) {
+        should_update_device_list = true;
+      } else {
+        DCHECK_EQ(XISlaveSwitch, xev->reason);
+        ui::DeviceDataManagerX11::GetInstance()->InvalidateScrollClasses(
+            xev->sourceid);

[sadrul, 2016/06/27 14:49:21]

Can |xev->sourceid| here be really -1?

[Will Shackleton, 2016/07/12 16:05:04]

There are other places |InvalidateScrollClasses| is called - see new change now
default parameter doesn't exist.

+      }
+    }
+  }
+
+  if (should_update_device_list) {
     UpdateDeviceList();
     hotplug_event_handler_->OnHotplugEvent();
   }