LibWeb: Absolutize internal lengths in all StyleValues

StyleValue now has a virtual visit_lengths() that allows us to update
all CSS lengths during the absolutization phase.

Userland/Libraries/LibWeb/CSS/StyleResolver.cpp

@@ -818,13 +818,12 @@ void StyleResolver::absolutize_values(StyleProperties& style, DOM::Element const
     float root_font_size = 10;
 
     for (auto& it : style.properties()) {
-        if (!it.value->is_length())
-            continue;
-        auto length = it.value->to_length();
-        if (length.is_relative()) {
-            auto px = length.relative_length_to_px(viewport_rect, font_metrics, root_font_size);
-            it.value = LengthStyleValue::create(CSS::Length::make_px(px));
-        }
+        it.value->visit_lengths([&](Length& length) {
+            if (length.is_absolute() || length.is_relative()) {
+                auto px = length.to_px(viewport_rect, font_metrics, root_font_size);
+                length = Length::make_px(px);
+            }
+        });
     }
 }
 

Userland/Libraries/LibWeb/CSS/StyleValue.h

@@ -8,6 +8,7 @@
 
 #pragma once
 
+#include <AK/Function.h>
 #include <AK/NonnullOwnPtr.h>
 #include <AK/NonnullOwnPtrVector.h>
 #include <AK/NonnullRefPtrVector.h>
@@ -357,6 +358,8 @@ public:
         return to_string() == other.to_string();
     }
 
+    virtual void visit_lengths(Function<void(CSS::Length&)>) { }
+
 protected:
     explicit StyleValue(Type);
 
@@ -514,12 +517,18 @@ private:
         m_is_elliptical = (m_horizontal_radius != m_vertical_radius);
     }
 
+    virtual void visit_lengths(Function<void(CSS::Length&)> visitor) override
+    {
+        visitor(m_horizontal_radius);
+        visitor(m_vertical_radius);
+    }
+
     bool m_is_elliptical;
     Length m_horizontal_radius;
     Length m_vertical_radius;
 };
 
-class BoxShadowStyleValue : public StyleValue {
+class BoxShadowStyleValue final : public StyleValue {
 public:
     static NonnullRefPtr<BoxShadowStyleValue> create(Length const& offset_x, Length const& offset_y, Length const& blur_radius, Color const& color)
     {
@@ -545,6 +554,13 @@ private:
     {
     }
 
+    virtual void visit_lengths(Function<void(CSS::Length&)> visitor) override
+    {
+        visitor(m_offset_x);
+        visitor(m_offset_y);
+        visitor(m_blur_radius);
+    }
+
     Length m_offset_x;
     Length m_offset_y;
     Length m_blur_radius;
@@ -964,6 +980,11 @@ private:
     {
     }
 
+    virtual void visit_lengths(Function<void(CSS::Length&)> visitor) override
+    {
+        visitor(m_length);
+    }
+
     Length m_length;
 };