mus: Let clients set the cursor of their window.

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 29b8ec14f1fada223e89bb103baca53ffffd9e49..ffe5fc2246a3f3a5dad67ca76a7edab5c160a3b3 100644
--- a/components/mus/ws/server_window.cc
+++ b/components/mus/ws/server_window.cc
@@ -29,6 +29,7 @@ ServerWindow::ServerWindow(ServerWindowDelegate* delegate,
       stacking_target_(nullptr),
       transient_parent_(nullptr),
       visible_(false),
+      cursor_id_(mojom::CURSOR_NULL),
       opacity_(1),
       can_focus_(true),
       properties_(properties),
@@ -261,6 +262,15 @@ void ServerWindow::SetOpacity(float value) {
   delegate_->OnScheduleWindowPaint(this);
 }
 
+void ServerWindow::SetPredefinedCursor(mus::mojom::Cursor value) {
+  if (value == cursor_id_)
+    return;
+  cursor_id_ = value;
+  FOR_EACH_OBSERVER(
+      ServerWindowObserver, observers_,
+      OnWindowSetPredefinedCursor(this, static_cast<int32_t>(value)));
+}
+
 void ServerWindow::SetTransform(const gfx::Transform& transform) {
   if (transform_ == transform)
     return;