Add a UMA histogram for a user's device scale at startup.

ui/display/win/screen_win.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_DISPLAY_WIN_SCREEN_WIN_H_
 #define UI_DISPLAY_WIN_SCREEN_WIN_H_
 
 #include <windows.h>
 
 #include <memory>
@@ skipping 149 matching lines @@
   ScreenWinDisplay GetScreenWinDisplay(const MONITORINFOEX& monitor_info) const;
 
   static float GetScaleFactorForHWND(HWND hwnd);
 
   // Returns the result of calling |getter| with |value| on the global
   // ScreenWin if it exists, otherwise return the default ScreenWinDisplay.
   template <typename Getter, typename GetterType>
   static ScreenWinDisplay GetScreenWinDisplayVia(Getter getter,
                                                  GetterType value);
 
+  void RecordDisplayScaleFactors() const;
+
   // Helper implementing the DisplayObserver handling.
   DisplayChangeNotifier change_notifier_;
 
   std::unique_ptr<gfx::SingletonHwndObserver> singleton_hwnd_observer_;
 
   // Current list of ScreenWinDisplays.
   std::vector<ScreenWinDisplay> screen_win_displays_;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenWin);
 };
 
 }  // namespace win
 }  // namespace display
 
 #endif  // UI_DISPLAY_WIN_SCREEN_WIN_H_