LibWeb/CSS: Expose method for parsing a type of StyleValue

In a few places, user code wants to parse a `<color>` or `<length>` etc,
but we didn't have a way to do so, so they would do something
similar-ish instead, like parse the value of the `color` property.
Let's make that available instead.

Author: AtkinsSJ

Libraries/LibWeb/CSS/Parser/Helpers.cpp

@@ -80,6 +80,13 @@ RefPtr<CSS::StyleValue const> parse_css_value(CSS::Parser::ParsingParams const&
     return CSS::Parser::Parser::create(context, string).parse_as_css_value(property_id);
 }
 
+RefPtr<CSS::StyleValue const> parse_css_type(CSS::Parser::ParsingParams const& context, StringView string, CSS::ValueType value_type)
+{
+    if (string.is_empty())
+        return nullptr;
+    return CSS::Parser::Parser::create(context, string).parse_as_type(value_type);
+}
+
 RefPtr<CSS::StyleValue const> parse_css_descriptor(CSS::Parser::ParsingParams const& parsing_params, CSS::AtRuleID at_rule_id, CSS::DescriptorID descriptor_id, StringView string)
 {
     if (string.is_empty())

Libraries/LibWeb/CSS/Parser/Parser.cpp

@@ -1742,6 +1742,13 @@ RefPtr<StyleValue const> Parser::parse_as_descriptor_value(AtRuleID at_rule_id,
     return parsed_value.release_value();
 }
 
+RefPtr<StyleValue const> Parser::parse_as_type(ValueType value_type)
+{
+    auto component_values = parse_a_list_of_component_values(m_token_stream);
+    TokenStream tokens { component_values };
+    return parse_value(value_type, tokens);
+}
+
 // https://html.spec.whatwg.org/multipage/images.html#parsing-a-sizes-attribute
 LengthOrCalculated Parser::parse_as_sizes_attribute(DOM::Element const& element, HTML::HTMLImageElement const* img)
 {

Libraries/LibWeb/CSS/Parser/Parser.h

@@ -151,6 +151,7 @@ class Parser {
 
     RefPtr<StyleValue const> parse_as_css_value(PropertyID);
     RefPtr<StyleValue const> parse_as_descriptor_value(AtRuleID, DescriptorID);
+    RefPtr<StyleValue const> parse_as_type(ValueType);
 
     Optional<ComponentValue> parse_as_component_value();
 
@@ -604,6 +605,7 @@ GC::Ref<CSS::CSSStyleSheet> parse_css_stylesheet(CSS::Parser::ParsingParams cons
 CSS::Parser::Parser::PropertiesAndCustomProperties parse_css_property_declaration_block(CSS::Parser::ParsingParams const&, StringView);
 Vector<CSS::Descriptor> parse_css_descriptor_declaration_block(CSS::Parser::ParsingParams const&, CSS::AtRuleID, StringView);
 RefPtr<CSS::StyleValue const> parse_css_value(CSS::Parser::ParsingParams const&, StringView, CSS::PropertyID);
+RefPtr<CSS::StyleValue const> parse_css_type(CSS::Parser::ParsingParams const&, StringView, CSS::ValueType);
 RefPtr<CSS::StyleValue const> parse_css_descriptor(CSS::Parser::ParsingParams const&, CSS::AtRuleID, CSS::DescriptorID, StringView);
 Optional<CSS::SelectorList> parse_selector(CSS::Parser::ParsingParams const&, StringView);
 Optional<CSS::SelectorList> parse_selector_for_nested_style_rule(CSS::Parser::ParsingParams const&, StringView);