Reduced number of UpdateDeviceList calls

ui/events/devices/x11/device_data_manager_x11.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/devices/x11/device_data_manager_x11.h"
 
 #include <stddef.h>
 #include <X11/extensions/XInput.h>
 #include <X11/extensions/XInput2.h>
 #include <X11/Xlib.h>
@@ skipping 542 matching lines @@
       continue;
     if (i == horizontal_number) {
       *x_offset = ExtractAndUpdateScrollOffset(&info->horizontal, *valuators);
     } else if (i == vertical_number) {
       *y_offset = ExtractAndUpdateScrollOffset(&info->vertical, *valuators);
     }
     valuators++;
   }
 }
 
-void DeviceDataManagerX11::InvalidateScrollClasses() {
-  for (int i = 0; i < kMaxDeviceNum; i++) {
-    scroll_data_[i].horizontal.seen = false;
-    scroll_data_[i].vertical.seen = false;
+void DeviceDataManagerX11::InvalidateScrollClasses(int device_id) {
+  if (device_id == -1) {
+    for (int i = 0; i < kMaxDeviceNum; i++) {
+      scroll_data_[i].horizontal.seen = false;
+      scroll_data_[i].vertical.seen = false;
+    }
+  } else {
+    if (device_id < 0 || device_id >= kMaxDeviceNum)
+      return;
+    scroll_data_[device_id].horizontal.seen = false;
+    scroll_data_[device_id].vertical.seen = false;
   }
 }
 
 void DeviceDataManagerX11::GetFlingData(const XEvent& xev,
                                         float* vx,
                                         float* vy,
                                         float* vx_ordinal,
                                         float* vy_ordinal,
                                         bool* is_cancel) {
   *vx = 0;
@@ skipping 303 matching lines @@
     } else {
       keyboards.erase(it);
       ++blocked_iter;
     }
   }
   // Notify base class of updated list.
   DeviceDataManager::OnKeyboardDevicesUpdated(keyboards);
 }
 
 }  // namespace ui