Makes Screen functions take a const gfx::NativeView

ash/display/screen_ash.cc

Index: ash/display/screen_ash.cc
diff --git a/ash/display/screen_ash.cc b/ash/display/screen_ash.cc
index bc1a81cf7da8eba43d3cbaf24536d33255005cc2..3424af469ba5c3b43d987a4df61070a989aa7a2b 100644
--- a/ash/display/screen_ash.cc
+++ b/ash/display/screen_ash.cc
@@ -49,7 +49,7 @@ class ScreenForShutdown : public display::Screen {
     return display_list_;
   }
   display::Display GetDisplayNearestWindow(
-      gfx::NativeView view) const override {
+      const gfx::NativeView view) const override {
     return primary_display_;
   }
   display::Display GetDisplayNearestPoint(
@@ -115,7 +115,7 @@ std::vector<display::Display> ScreenAsh::GetAllDisplays() const {
 }
 
 display::Display ScreenAsh::GetDisplayNearestWindow(
-    gfx::NativeView window) const {
+    const gfx::NativeView window) const {
   if (!window)
     return GetPrimaryDisplay();
   const aura::Window* root_window = window->GetRootWindow();