LibGUI: Make ToolBarContainer better at reacting to child events

Now you can remove a ToolBar from a ToolBarContainer and it will update
its own preferred size automatically.

Libraries/LibGUI/ToolBarContainer.cpp

@@ -32,9 +32,34 @@
 
 namespace GUI {
 
+void ToolBarContainer::child_event(Core::ChildEvent& event)
+{
+    Frame::child_event(event);
+
+    if (event.type() == Core::Event::ChildAdded) {
+        if (event.child() && event.child()->is_widget())
+            did_add_toolbar((Widget&)*event.child());
+    } else if (event.type() == Core::Event::ChildRemoved) {
+        if (event.child() && event.child()->is_widget()) {
+            did_remove_toolbar((Widget&)*event.child());
+        }
+    }
+}
+
+void ToolBarContainer::did_remove_toolbar(Widget& toolbar)
+{
+    m_toolbars.remove_first_matching([&](auto& entry) { return entry.ptr() == &toolbar; });
+    recompute_preferred_size();
+}
+
 void ToolBarContainer::did_add_toolbar(Widget& toolbar)
 {
     m_toolbars.append(toolbar);
+    recompute_preferred_size();
+}
+
+void ToolBarContainer::recompute_preferred_size()
+{
     int preferred_size = 4 + (m_toolbars.size() - 1) * 2;
 
     for (auto& toolbar : m_toolbars) {

Libraries/LibGUI/ToolBarContainer.h

@@ -35,20 +35,16 @@ class ToolBarContainer : public Frame {
     C_OBJECT(ToolBarContainer);
 
 public:
-    template<class T, class... Args>
-    inline T& add(Args&&... args)
-    {
-        auto& child = Frame::add<T>(forward<Args>(args)...);
-        did_add_toolbar(child);
-        return child;
-    }
 
 private:
     explicit ToolBarContainer(Gfx::Orientation = Gfx::Orientation::Horizontal);
 
     virtual void paint_event(GUI::PaintEvent&) override;
+    virtual void child_event(Core::ChildEvent&) override;
 
     void did_add_toolbar(Widget&);
+    void did_remove_toolbar(Widget&);
+    void recompute_preferred_size();
 
     Gfx::Orientation m_orientation { Gfx::Orientation::Horizontal };