LibWeb: Add CSS::Display enum and StyleProperties::display()

The display property is not interesting after we've built the layout
tree, so we don't have to move it into LayoutStyle.

Libraries/LibWeb/CSS/StyleProperties.cpp

@@ -244,4 +244,29 @@ CSS::TextAlign StyleProperties::text_align() const
     return CSS::TextAlign::Left;
 }
 
+CSS::Display StyleProperties::display() const
+{
+    auto display = string_or_fallback(CSS::PropertyID::Display, "inline");
+    if (display == "none")
+        return CSS::Display::None;
+    if (display == "block")
+        return CSS::Display::Block;
+    if (display == "inline")
+        return CSS::Display::Inline;
+    if (display == "inline-block")
+        return CSS::Display::InlineBlock;
+    if (display == "list-item")
+        return CSS::Display::ListItem;
+    if (display == "table")
+        return CSS::Display::Table;
+    if (display == "table-row")
+        return CSS::Display::TableRow;
+    if (display == "table-cell")
+        return CSS::Display::TableCell;
+    if (display == "table-row-group")
+        return CSS::Display::TableRowGroup;
+    dbg() << "Unknown display type: _" << display << "_";
+    return CSS::Display::Block;
+}
+
 }

Libraries/LibWeb/CSS/StyleProperties.h

@@ -60,6 +60,7 @@ public:
     String string_or_fallback(CSS::PropertyID, const StringView& fallback) const;
     Color color_or_fallback(CSS::PropertyID, const Document&, Color fallback) const;
     CSS::TextAlign text_align() const;
+    CSS::Display display() const;
 
     const Gfx::Font& font() const
     {

Libraries/LibWeb/CSS/StyleValue.h

@@ -123,6 +123,18 @@ enum class TextAlign {
     VendorSpecificCenter,
 };
 
+enum class Display {
+    None,
+    Block,
+    Inline,
+    InlineBlock,
+    ListItem,
+    Table,
+    TableRow,
+    TableCell,
+    TableRowGroup,
+};
+
 }
 
 class StyleValue : public RefCounted<StyleValue> {