Make aura::clients take Window instead of RootWindow

ash/display/screen_position_controller.cc

Index: ash/display/screen_position_controller.cc
diff --git a/ash/display/screen_position_controller.cc b/ash/display/screen_position_controller.cc
index 60528ec2955ca83fcc7a930727e68b22e7cf54d7..3713b78a1774e879c3615e336c15ffb56fb9581c 100644
--- a/ash/display/screen_position_controller.cc
+++ b/ash/display/screen_position_controller.cc
@@ -136,11 +136,12 @@ void ScreenPositionController::ConvertPointFromScreen(
 }
 
 void ScreenPositionController::ConvertHostPointToScreen(
-    aura::RootWindow* root_window,
+    aura::Window* root_window,
     gfx::Point* point) {
-  root_window->ConvertPointFromHost(point);
+  aura::RootWindow* root = root_window->GetRootWindow();
+  root->ConvertPointFromHost(point);
   std::pair<aura::RootWindow*, gfx::Point> pair =
-      GetRootWindowRelativeToWindow(root_window, *point);
+      GetRootWindowRelativeToWindow(root, *point);
   *point = pair.second;
   ConvertPointToScreen(pair.first, point);
 }