LibWeb: Implement CSS Angle class

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

Userland/Libraries/LibWeb/CSS/Angle.cpp

@@ -0,0 +1,99 @@
+/*
+ * Copyright (c) 2022, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "Angle.h"
+#include <AK/Math.h>
+#include <LibWeb/CSS/StyleValue.h>
+
+namespace Web::CSS {
+
+Angle::Angle(int value, Type type)
+    : m_type(type)
+    , m_value(value)
+{
+}
+
+Angle::Angle(float value, Type type)
+    : m_type(type)
+    , m_value(value)
+{
+}
+
+Angle Angle::make_calculated(NonnullRefPtr<CalculatedStyleValue> calculated_style_value)
+{
+    Angle angle { 0, Type::Calculated };
+    angle.m_calculated_style = move(calculated_style_value);
+    return angle;
+}
+
+Angle Angle::make_degrees(float value)
+{
+    return { value, Type::Deg };
+}
+
+Angle Angle::percentage_of(Percentage const& percentage) const
+{
+    VERIFY(!is_calculated());
+
+    return Angle { percentage.as_fraction() * m_value, m_type };
+}
+
+String Angle::to_string() const
+{
+    if (is_calculated())
+        return m_calculated_style->to_string();
+    return String::formatted("{}{}", m_value, unit_name());
+}
+
+float Angle::to_degrees() const
+{
+    switch (m_type) {
+    case Type::Calculated:
+        return m_calculated_style->resolve_angle()->to_degrees();
+    case Type::Deg:
+        return m_value;
+    case Type::Grad:
+        return m_value * (360.0f / 400.0f);
+    case Type::Rad:
+        return m_value * (360.0f / 2 * AK::Pi<float>);
+    case Type::Turn:
+        return m_value * 360.0f;
+    }
+    VERIFY_NOT_REACHED();
+}
+
+StringView Angle::unit_name() const
+{
+    switch (m_type) {
+    case Type::Calculated:
+        return "calculated"sv;
+    case Type::Deg:
+        return "deg"sv;
+    case Type::Grad:
+        return "grad"sv;
+    case Type::Rad:
+        return "rad"sv;
+    case Type::Turn:
+        return "turn"sv;
+    }
+    VERIFY_NOT_REACHED();
+}
+
+Optional<Angle::Type> Angle::unit_from_name(StringView name)
+{
+    if (name.equals_ignoring_case("deg"sv)) {
+        return Type::Deg;
+    } else if (name.equals_ignoring_case("grad"sv)) {
+        return Type::Grad;
+    } else if (name.equals_ignoring_case("rad"sv)) {
+        return Type::Rad;
+    } else if (name.equals_ignoring_case("turn"sv)) {
+        return Type::Turn;
+    }
+    return {};
+}
+
+}