LibWeb: Implement CSS Time class

This corresponds to `<time>` in the grammar.

Userland/Libraries/LibWeb/CSS/Time.cpp

@@ -0,0 +1,86 @@
+/*
+ * Copyright (c) 2022, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "Time.h"
+#include <LibWeb/CSS/StyleValue.h>
+
+namespace Web::CSS {
+
+Time::Time(int value, Type type)
+    : m_type(type)
+    , m_value(value)
+{
+}
+
+Time::Time(float value, Type type)
+    : m_type(type)
+    , m_value(value)
+{
+}
+
+Time Time::make_calculated(NonnullRefPtr<CalculatedStyleValue> calculated_style_value)
+{
+    Time frequency { 0, Type::Calculated };
+    frequency.m_calculated_style = move(calculated_style_value);
+    return frequency;
+}
+
+Time Time::make_seconds(float value)
+{
+    return { value, Type::S };
+}
+
+Time Time::percentage_of(Percentage const& percentage) const
+{
+    VERIFY(!is_calculated());
+
+    return Time { percentage.as_fraction() * m_value, m_type };
+}
+
+String Time::to_string() const
+{
+    if (is_calculated())
+        return m_calculated_style->to_string();
+    return String::formatted("{}{}", m_value, unit_name());
+}
+
+float Time::to_seconds() const
+{
+    switch (m_type) {
+    case Type::Calculated:
+        return m_calculated_style->resolve_time()->to_seconds();
+    case Type::S:
+        return m_value;
+    case Type::Ms:
+        return m_value / 1000.0f;
+    }
+    VERIFY_NOT_REACHED();
+}
+
+StringView Time::unit_name() const
+{
+    switch (m_type) {
+    case Type::Calculated:
+        return "calculated"sv;
+    case Type::S:
+        return "s"sv;
+    case Type::Ms:
+        return "ms"sv;
+    }
+    VERIFY_NOT_REACHED();
+}
+
+Optional<Time::Type> Time::unit_from_name(StringView name)
+{
+    if (name.equals_ignoring_case("s"sv)) {
+        return Type::S;
+    } else if (name.equals_ignoring_case("ms"sv)) {
+        return Type::Ms;
+    }
+    return {};
+}
+
+}