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

ash/display/multi_display_manager.cc

Index: ash/display/multi_display_manager.cc
diff --git a/ash/display/multi_display_manager.cc b/ash/display/multi_display_manager.cc
index e428c7c8654e4276f60b92f255ce015bda6ef5fc..cfa8d43448969d18c35e205e883c3ce6b04de3da 100644
--- a/ash/display/multi_display_manager.cc
+++ b/ash/display/multi_display_manager.cc
@@ -188,7 +188,8 @@ void MultiDisplayManager::OnNativeDisplaysChanged(
   std::vector<size_t> added_display_indices;
   gfx::Display current_primary;
   if (Shell::HasInstance())
-    current_primary = gfx::Screen::GetPrimaryDisplay();
+    current_primary = gfx::Screen::GetPrimaryDisplay(
+        ash::Shell::GetRootNativeView());
 
   for (DisplayList::iterator curr_iter = displays_.begin(),
        new_iter = new_displays.begin();