Remove now-unnecessary wrappers around gfx::Screen::GetScreen()

ash/dip_unittest.cc

Index: ash/dip_unittest.cc
diff --git a/ash/dip_unittest.cc b/ash/dip_unittest.cc
index a922da4200f2a29ce96aea4d504664dc919b5cc5..fc0066ab58ca2d79823097049fe6f8f2457485f2 100644
--- a/ash/dip_unittest.cc
+++ b/ash/dip_unittest.cc
@@ -37,7 +37,7 @@ TEST_F(DIPTest, WorkArea) {
 
   aura::Window* root = Shell::GetPrimaryRootWindow();
   const gfx::Display display =
-      Shell::GetScreen()->GetDisplayNearestWindow(root);
+      gfx::Screen::GetScreen()->GetDisplayNearestWindow(root);
 
   EXPECT_EQ("0,0 1000x900", display.bounds().ToString());
   gfx::Rect work_area = display.work_area();
@@ -45,7 +45,7 @@ TEST_F(DIPTest, WorkArea) {
   EXPECT_EQ("0,0,47,0", display.bounds().InsetsFrom(work_area).ToString());
 
   UpdateDisplay("2000x1800*2.0f");
-  gfx::Screen* screen = Shell::GetScreen();
+  gfx::Screen* screen = gfx::Screen::GetScreen();
 
   const gfx::Display display_2x = screen->GetDisplayNearestWindow(root);
   const DisplayInfo display_info_2x =