Create ScreenWin::GetSystemMetricsInDIP and Correctly Deprecate display::win::GetSystemMetricsInDIP

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 74 matching lines @@
   // The DPI scale is performed relative to the display nearest to |hwnd|.
   static gfx::Size ScreenToDIPSize(HWND hwnd, const gfx::Size& size_in_pixels);
 
   // Converts a DIP size to a physical size.
   // The DPI scale is performed relative to the display nearest to |hwnd|.
   static gfx::Size DIPToScreenSize(HWND hwnd, const gfx::Size& dip_size);
 
   // Returns the result of GetSystemMetrics for |metric| scaled to |hwnd|'s DPI.
   static int GetSystemMetricsForHwnd(HWND hwnd, int metric);
 
+  // Returns the result of GetSystemMetrics for |metric| in DIP.

[sky, 2016/07/27 21:44:11]

When would you use this rather than supplying an HWND and using it's scale?

[robliao, 2016/07/27 22:04:01]

You'd use this when you actually want to just do things in DIP. That turns out
to be HWND invariant.

GetSystemMetrics always returns results in physical pixels based off of the
primary monitor's DPI. If we removed GetSystemMetricsInDIP, to obtain the
equivalent result, you'd perform this calculation:
GetSystemMetricsForHwnd(hwnd, ...) / GetScaleFactorForHwnd(hwnd). This is
equivalent to

(GetSystemMetrics(metric) * HwndScaleFactor / PrimaryMonitorScaleFactor) /
HwndScaleFactor, leaving us with
GetSystemMetrics(metric) / PrimaryMonitorScaleFactor

Developers who need a physical metric for an HWND (like
BrowserDesktopWindowTreeHostWin's physical frame size) will want use
GetSystemMetricsForHwnd and avoid any rounding errors that arise from
GetSystemMetrics.

I've amended the comments to capture some of this.

+  static int GetSystemMetricsInDIP(int metric);
+
   // Returns |hwnd|'s scale factor.
   static float GetScaleFactorForHWND(HWND hwnd);
 
   // Returns the HWND associated with the NativeView.
   virtual HWND GetHWNDFromNativeView(gfx::NativeView window) const;
 
   // Returns the NativeView associated with the HWND.
   virtual gfx::NativeWindow GetNativeWindowFromHWND(HWND hwnd) const;
 
  protected:
@@ skipping 73 matching lines @@
   // 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_