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

ash/screensaver/screensaver_view.cc

Index: ash/screensaver/screensaver_view.cc
diff --git a/ash/screensaver/screensaver_view.cc b/ash/screensaver/screensaver_view.cc
index 3c89e66f58260746e3570d3e15db0597d4712919..89049cd5de8e39a22641d21c292b2f16e4a6b037 100644
--- a/ash/screensaver/screensaver_view.cc
+++ b/ash/screensaver/screensaver_view.cc
@@ -129,7 +129,7 @@ void ScreensaverView::LoadScreensaver() {
 void ScreensaverView::ShowWindow() {
   aura::RootWindow* root_window = ash::Shell::GetPrimaryRootWindow();
   gfx::Rect screen_rect =
-      gfx::Screen::GetDisplayNearestWindow(root_window).bounds();
+      Shell::GetAshScreen()->GetDisplayNearestWindow(root_window).bounds();
 
   // We want to be the fullscreen topmost child of the root window.
   // There should be nothing ever really that should show up on top of us.