Add a function to layout.h for getting ScaleFactor of the native view.

ui/base/layout.h

Index: ui/base/layout.h
diff --git a/ui/base/layout.h b/ui/base/layout.h
index 2349693779237879469147b2aa16407a8013bfb5..447dfacc1cada26bfdb75d26951aa1c0390c56e5 100644
--- a/ui/base/layout.h
+++ b/ui/base/layout.h
@@ -9,6 +9,7 @@
 
 #include "build/build_config.h"
 #include "ui/base/ui_export.h"
+#include "ui/gfx/native_widget_types.h"
 
 namespace ui {
 
@@ -49,6 +50,9 @@ UI_EXPORT float GetScaleFactorScale(ScaleFactor scale_factor);
 // little as possible.
 UI_EXPORT ScaleFactor GetScaleFactorFromScale(float scale);
 
+// Returns the ScaleFactor used by |view|.
+UI_EXPORT ScaleFactor GetScaleFactorForNativeView(gfx::NativeView view);
+
 #if defined(OS_MACOSX)
 
 // Returns a vector with the scale factors which are supported by this