LibWeb: Protect DOM node while preparing to send mouse events

The Help application was hooking HtmlView::on_link_click, which would
get invoked before DOM event dispatch. Since we were holding on to the
clicked node with a Node*, the DOM node was gone after returning from
the on_link_click callback.

Fix this by keeping DOM nodes in RefPtrs in the event management code.
Also move DOM event dispatch before widget hook invocation, to try and
keep things sane on the LibWeb side of things.

Fixes #1605.

Libraries/LibWeb/HtmlView.cpp

@@ -176,9 +176,9 @@ void HtmlView::mousemove_event(GUI::MouseEvent& event)
     auto result = layout_root()->hit_test(to_content_position(event.position()));
     const HTMLAnchorElement* hovered_link_element = nullptr;
     if (result.layout_node) {
-        auto* node = result.layout_node->node();
+        RefPtr<Node> node = result.layout_node->node();
         hovered_node_changed = node != document()->hovered_node();
-        document()->set_hovered_node(const_cast<Node*>(node));
+        document()->set_hovered_node(node);
         if (node) {
             hovered_link_element = node->enclosing_link_element();
             if (hovered_link_element) {
@@ -188,7 +188,7 @@ void HtmlView::mousemove_event(GUI::MouseEvent& event)
                 is_hovering_link = true;
             }
             auto offset = compute_mouse_event_offset(event.position(), *result.layout_node);
-            const_cast<Node*>(node)->dispatch_event(MouseEvent::create("mousemove", offset.x(), offset.y()));
+            node->dispatch_event(MouseEvent::create("mousemove", offset.x(), offset.y()));
         }
         if (m_in_mouse_selection) {
             layout_root()->selection().set_end({ result.layout_node, result.index_in_node });
@@ -200,7 +200,7 @@ void HtmlView::mousemove_event(GUI::MouseEvent& event)
         window()->set_override_cursor(is_hovering_link ? GUI::StandardCursor::Hand : GUI::StandardCursor::None);
     if (hovered_node_changed) {
         update();
-        auto* hovered_html_element = document()->hovered_node() ? document()->hovered_node()->enclosing_html_element() : nullptr;
+        RefPtr<HTMLElement> hovered_html_element = document()->hovered_node() ? document()->hovered_node()->enclosing_html_element() : nullptr;
         if (hovered_html_element && !hovered_html_element->title().is_null()) {
             auto screen_position = screen_relative_rect().location().translated(event.position());
             GUI::Application::the().show_tooltip(hovered_html_element->title(), screen_position.translated(4, 4));
@@ -224,11 +224,13 @@ void HtmlView::mousedown_event(GUI::MouseEvent& event)
     bool hovered_node_changed = false;
     auto result = layout_root()->hit_test(to_content_position(event.position()));
     if (result.layout_node) {
-        auto* node = result.layout_node->node();
+        RefPtr<Node> node = result.layout_node->node();
         hovered_node_changed = node != document()->hovered_node();
-        document()->set_hovered_node(const_cast<Node*>(node));
+        document()->set_hovered_node(node);
         if (node) {
-            if (auto* link = node->enclosing_link_element()) {
+            auto offset = compute_mouse_event_offset(event.position(), *result.layout_node);
+            node->dispatch_event(MouseEvent::create("mousedown", offset.x(), offset.y()));
+            if (RefPtr<HTMLAnchorElement> link = node->enclosing_link_element()) {
                 dbg() << "HtmlView: clicking on a link to " << link->href();
                 if (on_link_click)
                     on_link_click(link->href());
@@ -239,8 +241,6 @@ void HtmlView::mousedown_event(GUI::MouseEvent& event)
                     m_in_mouse_selection = true;
                 }
             }
-            auto offset = compute_mouse_event_offset(event.position(), *result.layout_node);
-            const_cast<Node*>(node)->dispatch_event(MouseEvent::create("mousedown", offset.x(), offset.y()));
         }
     }
     if (hovered_node_changed)
@@ -255,9 +255,9 @@ void HtmlView::mouseup_event(GUI::MouseEvent& event)
 
     auto result = layout_root()->hit_test(to_content_position(event.position()));
     if (result.layout_node) {
-        if (auto* node = result.layout_node->node()) {
+        if (RefPtr<Node> node = result.layout_node->node()) {
             auto offset = compute_mouse_event_offset(event.position(), *result.layout_node);
-            const_cast<Node*>(node)->dispatch_event(MouseEvent::create("mouseup", offset.x(), offset.y()));
+            node->dispatch_event(MouseEvent::create("mouseup", offset.x(), offset.y()));
         }
     }