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 bb9e73e8da3625c3cb026b5adb1086de0864a269..812a1e23ff3934128cca90563c9ecb66ae2a14ab 100644
--- a/chrome/browser/chromeos/display/primary_display_switch_observer.cc
+++ b/chrome/browser/chromeos/display/primary_display_switch_observer.cc
@@ -19,7 +19,8 @@ void PrimaryDisplaySwitchObserver::OnRootWindowMoved(
     const aura::RootWindow* root_window, const gfx::Point& new_origin) {
   PrefService* pref_service = ProfileManager::GetDefaultProfile()->GetPrefs();
   pref_service->SetInt64(
-      prefs::kPrimaryDisplayID, gfx::Screen::GetPrimaryDisplay().id());
+      prefs::kPrimaryDisplayID,
+      ash::Shell::GetAshScreen()->GetPrimaryDisplay().id());
 }
 
 PrimaryDisplaySwitchObserver::PrimaryDisplaySwitchObserver()