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

chrome/browser/chromeos/display/primary_display_switch_observer.cc

Index: chrome/browser/chromeos/display/primary_display_switch_observer.cc
diff --git a/chrome/browser/chromeos/display/primary_display_switch_observer.cc b/chrome/browser/chromeos/display/primary_display_switch_observer.cc
index 352edb389ac8babe74bf0b5b541af596cd5a1959..a3295fe1811c45f31ca5caeb8b02347a1f32f6da 100644
--- a/chrome/browser/chromeos/display/primary_display_switch_observer.cc
+++ b/chrome/browser/chromeos/display/primary_display_switch_observer.cc
@@ -16,8 +16,9 @@ namespace chromeos {
 
 void PrimaryDisplaySwitchObserver::OnRootWindowMoved(
     const aura::RootWindow* root_window, const gfx::Point& new_origin) {
-  StorePrimaryDisplayIDPref(ProfileManager::GetDefaultProfile()->GetPrefs(),
-                            gfx::Screen::GetPrimaryDisplay().id());
+  StorePrimaryDisplayIDPref(
+      ProfileManager::GetDefaultProfile()->GetPrefs(),
+      ash::Shell::GetAshScreen()->GetPrimaryDisplay().id());
 }
 
 PrimaryDisplaySwitchObserver::PrimaryDisplaySwitchObserver()