WIP: simplified display management in ash

ui/aura/mus/window_tree_host_mus_init_params.h

Index: ui/aura/mus/window_tree_host_mus_init_params.h
diff --git a/ui/aura/mus/window_tree_host_mus_init_params.h b/ui/aura/mus/window_tree_host_mus_init_params.h
index 0501d9b9b31041f7eacdef688a07989fce535e3e..990db07c87a5ed591f071619b048b54b48705ad2 100644
--- a/ui/aura/mus/window_tree_host_mus_init_params.h
+++ b/ui/aura/mus/window_tree_host_mus_init_params.h
@@ -13,8 +13,13 @@
 #include <vector>
 
 #include "cc/surfaces/frame_sink_id.h"
+#include "services/ui/public/interfaces/window_manager_constants.mojom.h"
 #include "ui/aura/aura_export.h"
 
+namespace display {
+class Display;
+}
+
 namespace aura {
 
 class WindowPortMus;
@@ -40,6 +45,12 @@ struct AURA_EXPORT WindowTreeHostMusInitParams {
 
   // Id of the display the window should be created on.
   int64_t display_id = 0;
+
+  // Only used when creating a WindowTreeHostMus for a display.
+  std::unique_ptr<display::Display> display;
+
+  // Only used when creating a WindowTreeHostMus in the window manager.
+  ui::mojom::WmViewportMetrics viewport_metrics;
 };
 
 // Creates a WindowTreeHostMusInitParams that is used when creating a top-level