mus: Send display-id to client only for the root windows.

components/mus/public/cpp/lib/window_tree_client_impl.h

Index: components/mus/public/cpp/lib/window_tree_client_impl.h
diff --git a/components/mus/public/cpp/lib/window_tree_client_impl.h b/components/mus/public/cpp/lib/window_tree_client_impl.h
index 74248abe40a9f951a43103ad4c9cc22303fad0f3..a35b2ea3cea43738982ed59cc8a297bd6758ce2f 100644
--- a/components/mus/public/cpp/lib/window_tree_client_impl.h
+++ b/components/mus/public/cpp/lib/window_tree_client_impl.h
@@ -167,6 +167,7 @@ class WindowTreeClientImpl : public WindowTreeConnection,
   void OnEmbedImpl(mojom::WindowTree* window_tree,
                    ClientSpecificId client_id,
                    mojom::WindowDataPtr root_data,
+                   int64_t display_id,
                    Id focused_window_id,
                    bool drawn);
 
@@ -189,6 +190,7 @@ class WindowTreeClientImpl : public WindowTreeConnection,
   void OnEmbed(ClientSpecificId client_id,
                mojom::WindowDataPtr root,
                mojom::WindowTreePtr tree,
+               int64_t display_id,
                Id focused_window_id,
                bool drawn) override;
   void OnEmbeddedAppDisconnected(Id window_id) override;
@@ -196,6 +198,7 @@ class WindowTreeClientImpl : public WindowTreeConnection,
   void OnLostCapture(Id window_id) override;
   void OnTopLevelCreated(uint32_t change_id,
                          mojom::WindowDataPtr data,
+                         int64_t display_id,
                          bool drawn) override;
   void OnWindowBoundsChanged(Id window_id,
                              mojo::RectPtr old_bounds,