LibHTML+Browser: Add debug option to draw borders around line boxes

This will be very useful when debugging line layout.

Applications/Browser/main.cpp

@@ -102,6 +102,15 @@ int main(int argc, char** argv)
     debug_menu->add_action(GAction::create("Dump Layout tree", [&](auto&) {
         dump_tree(*html_widget->document()->layout_node());
     }));
+    debug_menu->add_separator();
+    auto line_box_borders_action = GAction::create("Line box borders", [&](auto& action) {
+        action.set_checked(!action.is_checked());
+        html_widget->set_should_show_line_box_borders(action.is_checked());
+        html_widget->update();
+    });
+    line_box_borders_action->set_checkable(true);
+    line_box_borders_action->set_checked(false);
+    debug_menu->add_action(line_box_borders_action);
     menubar->add_menu(move(debug_menu));
 
     auto help_menu = make<GMenu>("Help");

Libraries/LibHTML/HtmlView.cpp

@@ -111,6 +111,7 @@ void HtmlView::paint_event(GPaintEvent& event)
     painter.translate(-horizontal_scrollbar().value(), -vertical_scrollbar().value());
 
     RenderingContext context { painter };
+    context.set_should_show_line_box_borders(m_should_show_line_box_borders);
     m_layout_root->render(context);
 }
 

Libraries/LibHTML/HtmlView.h

@@ -23,6 +23,8 @@ public:
 
     URL url() const;
 
+    void set_should_show_line_box_borders(bool value) { m_should_show_line_box_borders = value; }
+
     Function<void(const String&)> on_link_click;
     Function<void(const String&)> on_title_change;
     Function<void(const URL&)> on_load_start;
@@ -41,4 +43,6 @@ private:
     RefPtr<Frame> m_main_frame;
     RefPtr<Document> m_document;
     RefPtr<LayoutNode> m_layout_root;
+
+    bool m_should_show_line_box_borders { false };
 };

Libraries/LibHTML/Layout/LayoutBlock.cpp

@@ -204,6 +204,8 @@ void LayoutBlock::render(RenderingContext& context)
     if (children_are_inline()) {
         for (auto& line_box : m_line_boxes) {
             for (auto& fragment : line_box.fragments()) {
+                if (context.should_show_line_box_borders())
+                    context.painter().draw_rect(fragment.rect(), Color::Green);
                 fragment.render(context);
             }
         }

Libraries/LibHTML/RenderingContext.h

@@ -11,6 +11,10 @@ public:
 
     GPainter& painter() const { return m_painter; }
 
+    bool should_show_line_box_borders() const { return m_should_show_line_box_borders; }
+    void set_should_show_line_box_borders(bool value) { m_should_show_line_box_borders = value; }
+
 private:
     GPainter& m_painter;
+    bool m_should_show_line_box_borders { false };
 };