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

ui/display/win/dpi.h

Index: ui/display/win/dpi.h
diff --git a/ui/display/win/dpi.h b/ui/display/win/dpi.h
index 074eacadd5ec895ce902a3993f19c8bee992f98f..b792694c603f5b4cb710309b61c783046aca0c87 100644
--- a/ui/display/win/dpi.h
+++ b/ui/display/win/dpi.h
@@ -17,6 +17,9 @@ namespace win {
 // will be that returned by GetDPIScale().
 DISPLAY_EXPORT void SetDefaultDeviceScaleFactor(float scale);
 
+// Get the raw device scale value of the display, without clamping or forcing.
+DISPLAY_EXPORT float GetUnforcedDeviceScaleFactor();
+
 // Gets the scale factor of the display. For example, if the display DPI is
 // 96 then the scale factor is 1.0.  This clamps scale factors <= 1.25 to 1.0 to
 // maintain previous (non-DPI-aware) behavior where only the font size was