LibWeb: Support inline-level padding and border properly

Here's roughly how this works:

- InlineLevelIterator keeps a nesting stack of inline-level nodes with
  box model metrics.
- When entering a node with box model metrics, we add them to the
  current "leading metrics".
- When exiting a node with box model metrics, we add them to the
  current "trailing metrics".
- Pending leading metrics are consumed by the first fragment added
  to the line.
- Pending trailing metrics are consumed by the last fragment added
  to the line.

Like before, the position of a line box fragment is the top left of its
content box. However, fragments are placed horizontally along the line
with space inserted for padding and border.

InlineNode::paint() now expands the content rect as appropriate when
painting background and borders.

Note that margins and margin collapsing is not yet implemented.

This makes the eyes on ACID2 horizontally centered. :^)

Userland/Libraries/LibWeb/Layout/InlineNode.cpp

@@ -38,8 +38,20 @@ void InlineNode::paint(PaintContext& context, PaintPhase phase)
         auto bottom_left_border_radius = computed_values().border_bottom_left_radius();
         auto containing_block_position_in_absolute_coordinates = containing_block()->absolute_position();
 
-        for_each_fragment([&](auto const& fragment) {
+        for_each_fragment([&](auto const& fragment, bool is_first_fragment, bool is_last_fragment) {
             Gfx::FloatRect absolute_fragment_rect { containing_block_position_in_absolute_coordinates.translated(fragment.offset()), fragment.size() };
+
+            if (is_first_fragment) {
+                float extra_start_width = box_model().padding.left;
+                absolute_fragment_rect.translate_by(-extra_start_width, 0);
+                absolute_fragment_rect.set_width(absolute_fragment_rect.width() + extra_start_width);
+            }
+
+            if (is_last_fragment) {
+                float extra_end_width = box_model().padding.right;
+                absolute_fragment_rect.set_width(absolute_fragment_rect.width() + extra_end_width);
+            }
+
             auto border_radius_data = Painting::normalized_border_radius_data(*this, absolute_fragment_rect, top_left_border_radius, top_right_border_radius, bottom_right_border_radius, bottom_left_border_radius);
             Painting::paint_background(context, *this, enclosing_int_rect(absolute_fragment_rect), computed_values().background_color(), &computed_values().background_layers(), border_radius_data);
 
@@ -77,8 +89,20 @@ void InlineNode::paint(PaintContext& context, PaintPhase phase)
 
         auto containing_block_position_in_absolute_coordinates = containing_block()->absolute_position();
 
-        for_each_fragment([&](auto& fragment) {
+        for_each_fragment([&](auto const& fragment, bool is_first_fragment, bool is_last_fragment) {
             Gfx::FloatRect absolute_fragment_rect { containing_block_position_in_absolute_coordinates.translated(fragment.offset()), fragment.size() };
+
+            if (is_first_fragment) {
+                float extra_start_width = box_model().padding.left;
+                absolute_fragment_rect.translate_by(-extra_start_width, 0);
+                absolute_fragment_rect.set_width(absolute_fragment_rect.width() + extra_start_width);
+            }
+
+            if (is_last_fragment) {
+                float extra_end_width = box_model().padding.right;
+                absolute_fragment_rect.set_width(absolute_fragment_rect.width() + extra_end_width);
+            }
+
             auto bordered_rect = absolute_fragment_rect.inflated(borders_data.top.width, borders_data.right.width, borders_data.bottom.width, borders_data.left.width);
             auto border_radius_data = Painting::normalized_border_radius_data(*this, bordered_rect, top_left_border_radius, top_right_border_radius, bottom_right_border_radius, bottom_left_border_radius);
 
@@ -92,7 +116,7 @@ void InlineNode::paint(PaintContext& context, PaintPhase phase)
         // FIXME: This paints a double-thick border between adjacent fragments, where ideally there
         //        would be none. Once we implement non-rectangular outlines for the `outline` CSS
         //        property, we can use that here instead.
-        for_each_fragment([&](auto& fragment) {
+        for_each_fragment([&](auto& fragment, bool, bool) {
             painter.draw_rect(enclosing_int_rect(fragment.absolute_rect()), Color::Magenta);
             return IterationDecision::Continue;
         });
@@ -103,11 +127,16 @@ template<typename Callback>
 void InlineNode::for_each_fragment(Callback callback)
 {
     // FIXME: This will be slow if the containing block has a lot of fragments!
+    Vector<LineBoxFragment const&> fragments;
     containing_block()->for_each_fragment([&](auto& fragment) {
-        if (!is_inclusive_ancestor_of(fragment.layout_node()))
-            return IterationDecision::Continue;
-        return callback(fragment);
+        if (is_inclusive_ancestor_of(fragment.layout_node()))
+            fragments.append(fragment);
+        return IterationDecision::Continue;
     });
+    for (size_t i = 0; i < fragments.size(); ++i) {
+        auto const& fragment = fragments[i];
+        callback(fragment, i == 0, i == fragments.size() - 1);
+    }
 }
 
 }