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

ash/wm/window_manager_unittest.cc

Index: ash/wm/window_manager_unittest.cc
diff --git a/ash/wm/window_manager_unittest.cc b/ash/wm/window_manager_unittest.cc
index b99bbb841bd58effd0fd5f40d0d4f4d425ea3843..a84713898588548380fe7784cd1b8f42e018747b 100644
--- a/ash/wm/window_manager_unittest.cc
+++ b/ash/wm/window_manager_unittest.cc
@@ -466,7 +466,8 @@ TEST_F(WindowManagerTest, MAYBE_TransformActivate) {
   gfx::Size size = root_window->bounds().size();
   EXPECT_EQ(
       gfx::Rect(size).ToString(),
-      gfx::Screen::GetDisplayNearestPoint(gfx::Point()).bounds().ToString());
+      Shell::GetAshScreen()->GetDisplayNearestPoint(
+          gfx::Point()).bounds().ToString());
 
   // Rotate it clock-wise 90 degrees.
   ui::Transform transform;