Allow storing display preferences per device.

ash/test/ash_test_base.cc

Index: ash/test/ash_test_base.cc
diff --git a/ash/test/ash_test_base.cc b/ash/test/ash_test_base.cc
index 717bf51e641efe0ce6c9b5dd84518602e1123e46..7ac27fa8edfa6b3c12bb79cda27e7d0e587eca21 100644
--- a/ash/test/ash_test_base.cc
+++ b/ash/test/ash_test_base.cc
@@ -93,7 +93,7 @@ void AshTestBase::UpdateDisplay(const std::string& display_specs) {
   // On non-testing environment, when a secondary display is connected, a new
   // native (i.e. X) window for the display is always created below the previous
   // one for GPU performance reasons. Try to emulate the behavior.
-  if (internal::DisplayController::IsExtendedDesktopEnabled()) {
+  if (DisplayController::IsExtendedDesktopEnabled()) {
     Shell::RootWindowList root_windows = Shell::GetAllRootWindows();
     DCHECK_EQ(displays.size(), root_windows.size());
     size_t next_y = 0;