Add context to gfx::Screen calls in support of simultaneous desktop+ash

ash/screen_ash.cc

Index: ash/screen_ash.cc
diff --git a/ash/screen_ash.cc b/ash/screen_ash.cc
index efda02240d0849c533e6c4044d836a50d6bbb515..09eaf75ba6992b0599bd6022b01b3da9822af83c 100644
--- a/ash/screen_ash.cc
+++ b/ash/screen_ash.cc
@@ -96,7 +96,8 @@ gfx::Point ScreenAsh::GetCursorScreenPoint() {
 }
 
 gfx::NativeWindow ScreenAsh::GetWindowAtCursorScreenPoint() {
-  const gfx::Point point = gfx::Screen::GetCursorScreenPoint();
+  const gfx::Point point = gfx::Screen::GetCursorScreenPoint(
+      ash::Shell::GetRootNativeView());
   return wm::GetRootWindowAt(point)->GetTopWindowContainingPoint(point);
 }