Reduced number of UpdateDeviceList calls

ui/events/devices/x11/device_data_manager_x11.h

 // 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.
 
 #ifndef UI_EVENTS_DEVICES_X11_DEVICE_DATA_MANAGER_X11_H_
 #define UI_EVENTS_DEVICES_X11_DEVICE_DATA_MANAGER_X11_H_
 
 // Generically-named #defines from Xlib is conflicting with symbols in GTest.
 // So many tests .cc file #undef Bool before including device_data_manager.h,
 // which makes Bool unrecognized in XInput2.h.
@@ skipping 91 matching lines @@
     DT_TOUCH_TRACKING_ID,  // ID of the touch point.
 
     // Kernel timestamp from touch screen (if available).
     DT_TOUCH_RAW_TIMESTAMP,
 
     // End of touch data types.
 
     DT_LAST_ENTRY  // This must come last.
   };
 
+  // A Device ID number that can be passed to InvalidateScrollClasses that
+  // invalidates all devices.
+  static const int kAllDevices = -1;
+
   // Data struct to store extracted data from an input event.
   typedef std::map<int, double> EventData;
 
   static void CreateInstance();
 
   // We use int because enums can be casted to ints but not vice versa.
   static bool IsCMTDataType(const int type);
   static bool IsTouchDataType(const int type);
 
   // Returns the DeviceDataManagerX11 singleton.
@@ skipping 71 matching lines @@
                         int* finger_count);
 
   // Extract data from a scroll class event (smooth scrolling). User must
   // first verify the event type with GetScrollClassEventDetail.
   // Pointers shouldn't be NULL.
   void GetScrollClassOffsets(const XEvent& xev,
                              double* x_offset,
                              double* y_offset);
 
   // Invalidate stored scroll class counters, since they can change when
-  // pointing at other windows.
-  void InvalidateScrollClasses();
+  // pointing at other windows. If kAllDevices is specified, all devices are
+  // invalidated.
+  void InvalidateScrollClasses(int device_id);
 
   // Extract data from a fling event. User must first verify the event type
   // with IsFlingEvent. Pointers shouldn't be NULL.
   void GetFlingData(const XEvent& xev,
                     float* vx,
                     float* vy,
                     float* vx_ordinal,
                     float* vy_ordinal,
                     bool* is_cancel);
 
@@ skipping 175 matching lines @@
 
   unsigned char button_map_[256];
   int button_map_count_;
 
   DISALLOW_COPY_AND_ASSIGN(DeviceDataManagerX11);
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_DEVICES_X11_DEVICE_DATA_MANAGER_X11_H_