LibHTML: Add InheritStyleValue and InitialStyleValue.

These correspond to the 'inherit' and 'initial' CSS values respectively.

Libraries/LibHTML/CSS/StyleValue.h

@@ -20,6 +20,9 @@ public:
 
     Type type() const { return m_type; }
 
+    bool is_inherit() const { return type() == Type::Inherit; }
+    bool is_initial() const { return type() == Type::Initial; }
+
     virtual String to_string() const = 0;
 
 protected:
@@ -68,3 +71,31 @@ private:
 
     Length m_length;
 };
+
+class InitialStyleValue final : public StyleValue {
+public:
+    static NonnullRefPtr<InitialStyleValue> create() { return adopt(*new InitialStyleValue); }
+    virtual ~InitialStyleValue() override {}
+
+    String to_string() const override { return "initial"; }
+
+private:
+    InitialStyleValue()
+        : StyleValue(Type::Initial)
+    {
+    }
+};
+
+class InheritStyleValue final : public StyleValue {
+public:
+    static NonnullRefPtr<InheritStyleValue> create() { return adopt(*new InheritStyleValue); }
+    virtual ~InheritStyleValue() override {}
+
+    String to_string() const override { return "inherit"; }
+
+private:
+    InheritStyleValue()
+        : StyleValue(Type::Inherit)
+    {
+    }
+};

Libraries/LibHTML/Parser/CSSParser.cpp

@@ -13,6 +13,10 @@ NonnullRefPtr<StyleValue> parse_css_value(const StringView& view)
     unsigned as_uint = string.to_uint(ok);
     if (ok)
         return LengthStyleValue::create(Length(as_uint, Length::Type::Absolute));
+    if (string == "inherit")
+        return InheritStyleValue::create();
+    if (string == "initial")
+        return InitialStyleValue::create();
     if (string == "auto")
         return LengthStyleValue::create(Length());
     return StringStyleValue::create(string);