mus: Server-side implementation of modal windows

components/mus/ws/event_dispatcher.cc

Index: components/mus/ws/event_dispatcher.cc
diff --git a/components/mus/ws/event_dispatcher.cc b/components/mus/ws/event_dispatcher.cc
index ead61660ad570645411ad7e55eec1f77a37ee403..55717b553d90406d7974344f06d079abc2a2f7a6 100644
--- a/components/mus/ws/event_dispatcher.cc
+++ b/components/mus/ws/event_dispatcher.cc
@@ -52,6 +52,16 @@ bool IsLocationInNonclientArea(const ServerWindow* target,
   return true;
 }
 
+ServerWindow* GetModalTargetForWindow(ServerWindow* target) {
+  for (ServerWindow* window = target; window; window = window->parent()) {
+    for (const auto& transient_child : window->transient_children()) {
+      if (transient_child->is_modal())
+        return GetModalTargetForWindow(transient_child);
+    }
+  }
+  return target;
+}
+
 }  // namespace
 
 class EventMatcher {
@@ -443,10 +453,12 @@ EventDispatcher::PointerTarget EventDispatcher::PointerTargetForEvent(
     const ui::PointerEvent& event) const {
   PointerTarget pointer_target;
   gfx::Point location(event.location());
-  pointer_target.window =
+  ServerWindow* target_window =
       FindDeepestVisibleWindowForEvents(root_, surface_id_, &location);
+  pointer_target.window = GetModalTargetForWindow(target_window);
   pointer_target.is_mouse_event = event.IsMousePointerEvent();
   pointer_target.in_nonclient_area =
+      target_window != pointer_target.window ||
       IsLocationInNonclientArea(pointer_target.window, location);
   pointer_target.is_pointer_down = event.type() == ui::ET_POINTER_DOWN;
   return pointer_target;