x11: Move XInput2 availability information out of the message pump.

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_export.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];
   }
   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
 // round-trip time to the X server whenever such a device list is needed. The
 // update function will be called on each incoming XI_HierarchyChanged event.
-class EVENTS_EXPORT DeviceListCacheX {
+class EVENTS_BASE_EXPORT DeviceListCacheX {
  public:
   static DeviceListCacheX* GetInstance();
 
   void UpdateDeviceList(Display* display);
 
+  // Returns the list of devices associated with |display|. Uses the old X11
+  // protocol to get the list of the devices.
   const XDeviceList& GetXDeviceList(Display* display);
+
+  // Returns the list of devices associated with |display|. Uses the newer
+  // XINPUT2 protocol to get the list of devices. Before making this call, make
+  // sure that XInput2 support is available (e.g. by calling
+  // IsXInput2Available()).
   const XIDeviceList& GetXI2DeviceList(Display* display);
 
  private:
   friend struct DefaultSingletonTraits<DeviceListCacheX>;
 
   DeviceListCacheX();
   ~DeviceListCacheX();
 
   std::map<Display*, XDeviceList> x_dev_list_map_;
   std::map<Display*, XIDeviceList> xi_dev_list_map_;
 
-  bool xi2_;
-
   DISALLOW_COPY_AND_ASSIGN(DeviceListCacheX);
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_X_DEVICE_LIST_CACHE_X_H_