Revert of mus: Enable system modal windows

components/mus/ws/server_window.cc

Index: components/mus/ws/server_window.cc
diff --git a/components/mus/ws/server_window.cc b/components/mus/ws/server_window.cc
index 51d4faecdc18f253231133bb4d9ebf5e2d4c7ef4..eeb5d7d44929e0275c949faff176438dcd2b5b56 100644
--- a/components/mus/ws/server_window.cc
+++ b/components/mus/ws/server_window.cc
@@ -17,6 +17,28 @@
 namespace mus {
 
 namespace ws {
+
+namespace {
+
+const ServerWindow* GetModalChildForWindowAncestor(const ServerWindow* window) {
+  for (const ServerWindow* ancestor = window; ancestor;
+       ancestor = ancestor->parent()) {
+    for (const auto& transient_child : ancestor->transient_children()) {
+      if (transient_child->is_modal() && transient_child->IsDrawn())
+        return transient_child;
+    }
+  }
+  return nullptr;
+}
+
+const ServerWindow* GetModalTargetForWindow(const ServerWindow* window) {
+  const ServerWindow* modal_window = GetModalChildForWindowAncestor(window);
+  if (!modal_window)
+    return window;
+  return GetModalTargetForWindow(modal_window);
+}
+
+}  // namespace
 
 ServerWindow::ServerWindow(ServerWindowDelegate* delegate, const WindowId& id)
     : ServerWindow(delegate, id, Properties()) {}
@@ -206,11 +228,7 @@
   return nullptr;
 }
 
-bool ServerWindow::AddTransientWindow(ServerWindow* child) {
-  // A system modal window cannot become a transient child.
-  if (child->is_modal() && !child->transient_parent())
-    return false;
-
+void ServerWindow::AddTransientWindow(ServerWindow* child) {
   if (child->transient_parent())
     child->transient_parent()->RemoveTransientWindow(child);
 
@@ -226,7 +244,6 @@
 
   FOR_EACH_OBSERVER(ServerWindowObserver, observers_,
                     OnTransientWindowAdded(this, child));
-  return true;
 }
 
 void ServerWindow::RemoveTransientWindow(ServerWindow* child) {
@@ -249,6 +266,14 @@
 
 void ServerWindow::SetModal() {
   is_modal_ = true;
+}
+
+bool ServerWindow::IsBlockedByModalWindow() const {
+  return !!GetModalChildForWindowAncestor(this);
+}
+
+const ServerWindow* ServerWindow::GetModalTarget() const {
+  return GetModalTargetForWindow(this);
 }
 
 bool ServerWindow::Contains(const ServerWindow* window) const {