LibWeb: Replace Length::set_calculated_style() with ::make_calculated()

There's no need to modify the Length's calculated-value after creating
it, so let's make it immutable. :^)

Userland/Libraries/LibWeb/CSS/Length.cpp

@@ -40,6 +40,13 @@ Length Length::make_px(float value)
     return Length(value, Type::Px);
 }
 
+Length Length::make_calculated(NonnullRefPtr<CalculatedStyleValue> calculated_style_value)
+{
+    Length length { 0, Type::Calculated };
+    length.m_calculated_style = move(calculated_style_value);
+    return length;
+}
+
 Length Length::percentage_of(Percentage const& percentage) const
 {
     if (is_undefined_or_auto()) {
@@ -71,11 +78,6 @@ Length Length::resolved_or_zero(Layout::Node const& layout_node) const
     return resolved(make_px(0), layout_node);
 }
 
-void Length::set_calculated_style(CalculatedStyleValue* value)
-{
-    m_calculated_style = value;
-}
-
 float Length::relative_length_to_px(Gfx::IntRect const& viewport_rect, Gfx::FontMetrics const& font_metrics, float root_font_size) const
 {
     switch (m_type) {

Userland/Libraries/LibWeb/CSS/Length.h

@@ -43,6 +43,7 @@ public:
 
     static Length make_auto();
     static Length make_px(float value);
+    static Length make_calculated(NonnullRefPtr<CalculatedStyleValue>);
     Length percentage_of(Percentage const&) const;
 
     Length resolved(Length const& fallback_for_undefined, Layout::Node const& layout_node) const;
@@ -131,8 +132,6 @@ public:
         return !(*this == other);
     }
 
-    void set_calculated_style(CalculatedStyleValue* value);
-
     float relative_length_to_px(Gfx::IntRect const& viewport_rect, Gfx::FontMetrics const& font_metrics, float root_font_size) const;
 
 private:

Userland/Libraries/LibWeb/CSS/StyleComputer.cpp

@@ -773,9 +773,7 @@ void StyleComputer::compute_font(StyleProperties& style, DOM::Element const* ele
             maybe_length = font_size->to_length();
 
         } else if (font_size->is_calculated()) {
-            Length length = Length(0, Length::Type::Calculated);
-            length.set_calculated_style(verify_cast<CalculatedStyleValue>(font_size.ptr()));
-            maybe_length = length;
+            maybe_length = Length::make_calculated(font_size->as_calculated());
         }
         if (maybe_length.has_value()) {
             // FIXME: Support font-size: calc(...)

Userland/Libraries/LibWeb/CSS/StyleProperties.cpp

@@ -54,11 +54,8 @@ Length StyleProperties::length_or_fallback(CSS::PropertyID id, Length const& fal
         return fallback;
     auto& value = maybe_value.value();
 
-    if (value->is_calculated()) {
-        Length length = Length(0, Length::Type::Calculated);
-        length.set_calculated_style(&value->as_calculated());
-        return length;
-    }
+    if (value->is_calculated())
+        return Length::make_calculated(value->as_calculated());
 
     if (value->has_length())
         return value->to_length();
@@ -75,9 +72,7 @@ LengthPercentage StyleProperties::length_percentage_or_fallback(CSS::PropertyID
 
     if (value->is_calculated()) {
         // FIXME: Handle percentages here
-        Length length = Length(0, Length::Type::Calculated);
-        length.set_calculated_style(&value->as_calculated());
-        return length;
+        return Length::make_calculated(value->as_calculated());
     }
 
     if (value->is_percentage())