ui: Forward declare DefaultSingletonTraits in header files.

ui/base/x/valuators.cc

 // 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.
 
 #include "ui/base/x/valuators.h"
 
 #include <X11/extensions/XInput2.h>
 
+#include "base/memory/singleton.h"
+#include "ui/base/touch/touch_factory.h"
 #include "ui/base/x/x11_util.h"
-#include "ui/base/touch/touch_factory.h"
 
 namespace {
 
 #define AXIS_LABEL_ABS_MT_TOUCH_MAJOR "Abs MT Touch Major"
 #define AXIS_LABEL_ABS_MT_TOUCH_MINOR "Abs MT Touch Minor"
 #define AXIS_LABEL_ABS_MT_ORIENTATION "Abs MT Orientation"
 #define AXIS_LABEL_ABS_MT_PRESSURE    "Abs MT Pressure"
 #define AXIS_LABEL_ABS_MT_SLOT_ID     "Abs MT Slot ID"
 #define AXIS_LABEL_ABS_MT_TRACKING_ID "Abs MT Tracking ID"
 
@@ skipping 152 matching lines @@
         valuator_max_[info->deviceid][j] = valuator->max;
       }
     }
   }
 
   if (info_list)
     XIFreeDeviceInfo(info_list);
 }
 
 }  // namespace ui