ui: Forward declare DefaultSingletonTraits in header files.

ui/base/x/valuators.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_X_VALUATORS_H_
 #define UI_BASE_X_VALUATORS_H_
 
-#include <map>
+#include "base/basictypes.h"
 
-#include "base/memory/singleton.h"
+template <typename T> struct DefaultSingletonTraits;
 
 typedef union _XEvent XEvent;
 
 namespace ui {
 
 // A valuator is not reported in an XEvent if it hasn't changed from the
 // previous event from the same device. As a result, it is necessary to track
 // the last reported valuator values for a specific device.
 // Right now, this is only used to keep track of valuators for events coming in
 // from touch-devices, but it can be used for other devices as well.
@@ skipping 83 matching lines @@
   // a device. Defaults to 0 if the valuator was not specified in an earlier
   // event.
   float last_seen_valuator_[kMaxDeviceNum][VAL_LAST_ENTRY];
 
   DISALLOW_COPY_AND_ASSIGN(ValuatorTracker);
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_X_VALUATORS_H_