LibWeb/CSS: Add has_property() to CSSStyleDeclaration

This isn't part of the CSSOM API directly, but will be used by
StylePropertyMapReadOnly.has() to avoid doing the work to serialize a
string version of the property's value, just to throw it away again.

Libraries/LibWeb/CSS/CSSDescriptors.cpp

@@ -281,6 +281,14 @@ RefPtr<StyleValue const> CSSDescriptors::descriptor_or_initial_value(DescriptorI
     return descriptor_initial_value(m_at_rule_id, descriptor_id);
 }
 
+bool CSSDescriptors::has_property(StringView property_name) const
+{
+    auto descriptor_id = descriptor_id_from_string(m_at_rule_id, property_name);
+    if (!descriptor_id.has_value())
+        return false;
+    return descriptor(*descriptor_id) != nullptr;
+}
+
 bool is_shorthand(AtRuleID at_rule, DescriptorID descriptor)
 {
     if (at_rule == AtRuleID::Page && descriptor == DescriptorID::Margin)

Libraries/LibWeb/CSS/CSSDescriptors.h

@@ -33,6 +33,8 @@ public:
 
     virtual WebIDL::ExceptionOr<void> set_css_text(StringView) override;
 
+    virtual bool has_property(StringView property_name) const override;
+
 protected:
     CSSDescriptors(JS::Realm&, AtRuleID, Vector<Descriptor>);
 

Libraries/LibWeb/CSS/CSSStyleDeclaration.h

@@ -57,6 +57,8 @@ public:
     [[nodiscard]] bool is_updating() const { return m_updating; }
     void set_is_updating(bool value) { m_updating = value; }
 
+    virtual bool has_property(StringView property_name) const = 0;
+
 protected:
     enum class Computed : u8 {
         No,

Libraries/LibWeb/CSS/CSSStyleProperties.cpp

@@ -426,6 +426,14 @@ StringView CSSStyleProperties::get_property_priority(StringView property_name) c
     return maybe_property->important == Important::Yes ? "important"sv : ""sv;
 }
 
+bool CSSStyleProperties::has_property(StringView property_name) const
+{
+    auto property_id = property_id_from_string(property_name);
+    if (!property_id.has_value())
+        return false;
+    return get_property_internal(*property_id).has_value();
+}
+
 // https://drafts.csswg.org/cssom/#dom-cssstyledeclaration-getpropertyvalue
 Optional<StyleProperty> CSSStyleProperties::get_property_internal(PropertyID property_id) const
 {

Libraries/LibWeb/CSS/CSSStyleProperties.h

@@ -49,6 +49,8 @@ public:
 
     size_t custom_property_count() const { return m_custom_properties.size(); }
 
+    virtual bool has_property(StringView property_name) const override;
+
     String css_float() const;
     WebIDL::ExceptionOr<void> set_css_float(StringView);