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

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 3f2c39200cbf24c4a70f67a7536f268b23e38c54..b87a62ae04ee656d938e7ca20eabc7e8285fae71 100644
--- a/ash/display/screen_position_controller.cc
+++ b/ash/display/screen_position_controller.cc
@@ -62,7 +62,7 @@ void ScreenPositionController::ConvertPointToScreen(
   const aura::RootWindow* root = window->GetRootWindow();
   aura::Window::ConvertPointToTarget(window, root, point);
   const gfx::Point display_origin =
-      gfx::Screen::GetDisplayNearestWindow(
+      Shell::GetAshScreen()->GetDisplayNearestWindow(
           const_cast<aura::RootWindow*>(root)).bounds().origin();
   point->Offset(display_origin.x(), display_origin.y());
 }
@@ -72,7 +72,7 @@ void ScreenPositionController::ConvertPointFromScreen(
     gfx::Point* point) {
   const aura::RootWindow* root = window->GetRootWindow();
   const gfx::Point display_origin =
-      gfx::Screen::GetDisplayNearestWindow(
+      Shell::GetAshScreen()->GetDisplayNearestWindow(
           const_cast<aura::RootWindow*>(root)).bounds().origin();
   point->Offset(-display_origin.x(), -display_origin.y());
   aura::Window::ConvertPointToTarget(root, window, point);
@@ -150,8 +150,8 @@ void ScreenPositionController::SetBounds(aura::Window* window,
   }
 
   gfx::Point origin(bounds.origin());
-  const gfx::Point display_origin =
-      gfx::Screen::GetDisplayNearestWindow(window).bounds().origin();
+  const gfx::Point display_origin = Shell::GetAshScreen()->
+      GetDisplayNearestWindow(window).bounds().origin();
   origin.Offset(-display_origin.x(), -display_origin.y());
   window->SetBounds(gfx::Rect(origin, bounds.size()));
 }