ui: Forward declare DefaultSingletonTraits in header files.

ui/base/touch/touch_factory.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_BASE_TOUCH_TOUCH_FACTORY_H_
 #define UI_BASE_TOUCH_TOUCH_FACTORY_H_
 
 #include <bitset>
 #include <map>
 #include <vector>
 
-#include "base/memory/singleton.h"
 #include "base/hash_tables.h"
 #include "base/timer.h"
 #include "ui/base/ui_export.h"
 
+template <typename T> struct DefaultSingletonTraits;
+
 typedef unsigned long Cursor;
 typedef unsigned long Window;
 typedef struct _XDisplay Display;
 typedef union _XEvent XEvent;
 
 namespace ui {
 
 // Functions related to determining touch devices.
 class UI_EXPORT TouchFactory {
  private:
@@ skipping 137 matching lines @@
 
   // A lookup table for slots in use for a touch event.
   std::bitset<kMaxTouchPoints> slots_used_;
 
   DISALLOW_COPY_AND_ASSIGN(TouchFactory);
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_TOUCH_TOUCH_FACTORY_H_