LibWeb: Make TextNode::ChunkIterator emit an empty chunk for content:""

This ensures that we create a line box for content:"", which would
otherwise get pruned by the empty line cleanup in IFC.

The empty line box is important in this case, since it gives us a
reference point for measuring the automatic height of the IFC's
containing block. By having an empty line, we can now correctly measure
the impact of vertical margins on a generated box with content:""
and allow them to contribute to the block height.

Userland/Libraries/LibWeb/Layout/InlineLevelIterator.cpp

@@ -264,7 +264,7 @@ void InlineLevelIterator::enter_text_node(Layout::TextNode const& text_node)
         .do_respect_linebreaks = do_respect_linebreaks,
         .is_first_chunk = true,
         .is_last_chunk = false,
-        .chunk_iterator = TextNode::ChunkIterator { text_node.text_for_rendering(), do_wrap_lines, do_respect_linebreaks },
+        .chunk_iterator = TextNode::ChunkIterator { text_node.text_for_rendering(), do_wrap_lines, do_respect_linebreaks, text_node.is_generated() && text_node.text_for_rendering().is_empty() },
     };
     m_text_node_context->next_chunk = m_text_node_context->chunk_iterator.next();
 }

Userland/Libraries/LibWeb/Layout/TextNode.cpp

@@ -85,9 +85,10 @@ void TextNode::compute_text_for_rendering(bool collapse)
     m_text_for_rendering = builder.to_string();
 }
 
-TextNode::ChunkIterator::ChunkIterator(StringView text, bool wrap_lines, bool respect_linebreaks)
+TextNode::ChunkIterator::ChunkIterator(StringView text, bool wrap_lines, bool respect_linebreaks, bool is_generated_empty_string)
     : m_wrap_lines(wrap_lines)
     , m_respect_linebreaks(respect_linebreaks)
+    , m_should_emit_one_empty_chunk(is_generated_empty_string)
     , m_utf8_view(text)
     , m_iterator(m_utf8_view.begin())
 {
@@ -95,6 +96,17 @@ TextNode::ChunkIterator::ChunkIterator(StringView text, bool wrap_lines, bool re
 
 Optional<TextNode::Chunk> TextNode::ChunkIterator::next()
 {
+    if (m_should_emit_one_empty_chunk) {
+        m_should_emit_one_empty_chunk = false;
+        return Chunk {
+            .view = {},
+            .start = 0,
+            .length = 0,
+            .has_breaking_newline = false,
+            .is_all_whitespace = false,
+        };
+    }
+
     if (m_iterator == m_utf8_view.end())
         return {};
 

Userland/Libraries/LibWeb/Layout/TextNode.h

@@ -33,7 +33,7 @@ public:
 
     class ChunkIterator {
     public:
-        ChunkIterator(StringView text, bool wrap_lines, bool respect_linebreaks);
+        ChunkIterator(StringView text, bool wrap_lines, bool respect_linebreaks, bool is_generated_empty_string);
         Optional<Chunk> next();
 
     private:
@@ -41,6 +41,7 @@ public:
 
         bool const m_wrap_lines;
         bool const m_respect_linebreaks;
+        bool m_should_emit_one_empty_chunk { false };
         Utf8View m_utf8_view;
         Utf8View::Iterator m_iterator;
     };