chromeos: changes how DisplayManagerObservers are notified

ui/aura/mus/window_manager_delegate.h

Index: ui/aura/mus/window_manager_delegate.h
diff --git a/ui/aura/mus/window_manager_delegate.h b/ui/aura/mus/window_manager_delegate.h
index e1876e568a8db464dd6332d4987bedacab7d4a66..8ba30ad21fbf8c663eb0257fb78c9bff0c2baa6a 100644
--- a/ui/aura/mus/window_manager_delegate.h
+++ b/ui/aura/mus/window_manager_delegate.h
@@ -91,6 +91,13 @@ class AURA_EXPORT WindowManagerClient {
   // DisplayInitParams on the returned object.
   virtual WindowTreeHostMusInitParams CreateInitParamsForNewDisplay() = 0;
 
+  // Configures the displays. This is used when the window manager manually
+  // configures display roots.
+  virtual void SetDisplayConfiguration(
+      const std::vector<display::Display>& displays,
+      std::vector<ui::mojom::WmViewportMetricsPtr> viewport_metrics,
+      int64_t primary_display_id) = 0;
+
  protected:
   virtual ~WindowManagerClient() {}
 };