mus: Server-side implementation of modal windows

components/mus/ws/server_window.h

Index: components/mus/ws/server_window.h
diff --git a/components/mus/ws/server_window.h b/components/mus/ws/server_window.h
index 46a1b21b81a798ccc661821f08527a3adf336c5b..e8a0f3520905c70884b57598284c956cd3e7982c 100644
--- a/components/mus/ws/server_window.h
+++ b/components/mus/ws/server_window.h
@@ -108,6 +108,9 @@ class ServerWindow {
 
   const Windows& transient_children() const { return transient_children_; }
 
+  bool is_modal() const { return is_modal_; }
+  void SetAsModal();
+
   // Returns true if this contains |window| or is |window|.
   bool Contains(const ServerWindow* window) const;
 
@@ -197,6 +200,7 @@ class ServerWindow {
   ServerWindow* transient_parent_;
   Windows transient_children_;
 
+  bool is_modal_;
   bool visible_;
   gfx::Rect bounds_;
   gfx::Insets client_area_;