Move touchscreen device caching to DeviceDataManager

ui/events/x/device_list_cache_x.h

 // Copyright (c) 2012 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_X_DEVICE_LIST_CACHE_X_H_
 #define UI_EVENTS_X_DEVICE_LIST_CACHE_X_H_
 
 #include <X11/extensions/XInput.h>
 #include <X11/extensions/XInput2.h>
 
 #include <map>
 
 #include "base/basictypes.h"
 #include "ui/events/events_base_export.h"
 
 template <typename T> struct DefaultSingletonTraits;
 
 typedef struct _XDisplay Display;
 
 template <typename T>
 struct DeviceList {
   DeviceList() : devices(NULL), count(0) {
   }
   T& operator[] (int x) {
     return devices[x];
   }
+  const T& operator[](int x) const { return devices[x]; }
   T* devices;
   int count;
 };
 
 typedef struct DeviceList<XDeviceInfo> XDeviceList;
 typedef struct DeviceList<XIDeviceInfo> XIDeviceList;
 
 namespace ui {
 
 // A class to cache the current XInput device list. This minimized the
@@ skipping 24 matching lines @@
   std::map<Display*, XDeviceList> x_dev_list_map_;
   std::map<Display*, XIDeviceList> xi_dev_list_map_;
 
   DISALLOW_COPY_AND_ASSIGN(DeviceListCacheX);
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_X_DEVICE_LIST_CACHE_X_H_