Move DisplayList to display; add ScreenBase.

ash/display/mirror_window_controller.cc

Index: ash/display/mirror_window_controller.cc
diff --git a/ash/display/mirror_window_controller.cc b/ash/display/mirror_window_controller.cc
index fec84ea72e6a211e1c423f37db6f7c81c133c25c..60b17151f7107f9ac1d3bfdec243945c71800e98 100644
--- a/ash/display/mirror_window_controller.cc
+++ b/ash/display/mirror_window_controller.cc
@@ -333,10 +333,9 @@ display::Display MirrorWindowController::GetDisplayForRootWindow(
     if (pair.second->ash_host->AsWindowTreeHost()->window() == root) {
       // Sanity check to catch an error early.
       int64_t id = pair.first;
-      const display::DisplayList& list =
-          Shell::GetInstance()
-              ->display_manager()
-              ->software_mirroring_display_list();
+      const display::Displays& list = Shell::GetInstance()
+                                          ->display_manager()
+                                          ->software_mirroring_display_list();
       auto iter = std::find_if(
           list.begin(), list.end(),
           [id](const display::Display& display) { return display.id() == id; });