mus: Use TooltipManagerAura in NativeWidgetMus.

ui/views/mus/window_manager_connection.cc

Index: ui/views/mus/window_manager_connection.cc
diff --git a/ui/views/mus/window_manager_connection.cc b/ui/views/mus/window_manager_connection.cc
index 8c4cf85d690d545d2fa9dd9e3da5723597200e45..446c9eafd0fbd9420154073b14e2a728bf2e46e1 100644
--- a/ui/views/mus/window_manager_connection.cc
+++ b/ui/views/mus/window_manager_connection.cc
@@ -167,6 +167,15 @@ gfx::Point WindowManagerConnection::GetCursorScreenPoint() {
   return client_->GetCursorScreenPoint();
 }
 
+ui::Window* WindowManagerConnection::GetWindowAtScreenPoint(
+    const gfx::Point& point) {
+  for (ui::Window* root : GetRoots()) {
+    if (root->bounds().Contains(point))
+      return root;
+  }
+  return nullptr;
+}
+
 std::unique_ptr<OSExchangeData::Provider>
 WindowManagerConnection::BuildProvider() {
   return base::MakeUnique<OSExchangeDataProviderMus>();