Tab dragging as implemented as a mus API.

components/mus/public/cpp/lib/window.cc

Index: components/mus/public/cpp/lib/window.cc
diff --git a/components/mus/public/cpp/lib/window.cc b/components/mus/public/cpp/lib/window.cc
index e117fe651ffadf145f975a345fbc60c41f5e779b..a02eccbfcd87837977a1ba583c8301bfb5de9b17 100644
--- a/components/mus/public/cpp/lib/window.cc
+++ b/components/mus/public/cpp/lib/window.cc
@@ -464,6 +464,14 @@ void Window::RequestClose() {
     client_->RequestClose(this);
 }
 
+bool Window::PerformWindowMove(const gfx::Point& cursor_location) {
+  return client_->PerformWindowMove(this, cursor_location);
+}
+
+void Window::CancelWindowMove() {
+  client_->CancelWindowMove(this);
+}
+
 std::string Window::GetName() const {
   if (HasSharedProperty(mojom::WindowManager::kName_Property))
     return GetSharedProperty<std::string>(mojom::WindowManager::kName_Property);