LibWeb: Add CSS.escape() JS function

This is the `CSS` namespace defined in IDL here:
https://www.w3.org/TR/cssom-1/#namespacedef-css , not to be confused
with our `Web::CSS` namespace. Words are hard.

`CSS.escape()` lets you escape identifiers that can then be used to
create a CSS string.

I've also stubbed out the `CSS.supports()` function.

Userland/Libraries/LibWeb/Bindings/CSSNamespace.cpp

@@ -0,0 +1,75 @@
+/*
+ * Copyright (c) 2021, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/Runtime/ErrorTypes.h>
+#include <LibJS/Runtime/GlobalObject.h>
+#include <LibJS/Runtime/VM.h>
+#include <LibJS/Runtime/Value.h>
+#include <LibWeb/Bindings/CSSNamespace.h>
+
+namespace Web::Bindings {
+
+CSSNamespace::CSSNamespace(JS::GlobalObject& global_object)
+    : JS::Object(*global_object.object_prototype())
+{
+}
+
+CSSNamespace::~CSSNamespace()
+{
+}
+
+void CSSNamespace::initialize(JS::GlobalObject& global_object)
+{
+    Object::initialize(global_object);
+    u8 attr = JS::Attribute::Enumerable;
+    define_native_function("escape", escape, 1, attr);
+    define_native_function("supports", supports, 2, attr);
+}
+
+// https://www.w3.org/TR/cssom-1/#dom-css-escape
+JS_DEFINE_NATIVE_FUNCTION(CSSNamespace::escape)
+{
+    if (!vm.argument_count()) {
+        vm.throw_exception<JS::TypeError>(global_object, JS::ErrorType::BadArgCountAtLeastOne, "CSS.escape");
+        return {};
+    }
+
+    String result = Web::CSS::serialize_an_identifier(vm.argument(0).to_string(global_object));
+    if (vm.exception())
+        return {};
+
+    return JS::Value(JS::js_string(vm, result));
+}
+
+// https://www.w3.org/TR/css-conditional-3/#dom-css-supports
+JS_DEFINE_NATIVE_FUNCTION(CSSNamespace::supports)
+{
+    if (!vm.argument_count()) {
+        vm.throw_exception<JS::TypeError>(global_object, JS::ErrorType::BadArgCountAtLeastOne, "CSS.supports");
+        return {};
+    }
+
+    if (vm.argument_count() >= 2) {
+        // When the supports(property, value) method is invoked with two arguments property and value:
+        //     If property is an ASCII case-insensitive match for any defined CSS property that the UA supports, and value successfully parses according to that property’s grammar, return true.
+        //
+        //     Otherwise, if property is a custom property name string, return true.
+        //
+        //     Otherwise, return false.
+        return JS::Value(false);
+    } else {
+        // When the supports(conditionText) method is invoked with a single conditionText argument:
+        //
+        //    If conditionText, parsed and evaluated as a <supports-condition>, would return true, return true.
+        //
+        //    Otherwise, If conditionText, wrapped in parentheses and then parsed and evaluated as a <supports-condition>, would return true, return true.
+        //
+        //    Otherwise, return false.
+        return JS::Value(false);
+    }
+}
+
+}

Userland/Libraries/LibWeb/Bindings/CSSNamespace.h

@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) 2021, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibJS/Runtime/Object.h>
+#include <LibWeb/CSS/Serialize.h>
+
+namespace Web::Bindings {
+
+// The `CSS` namespace object in IDL. https://www.w3.org/TR/cssom-1/#namespacedef-css
+class CSSNamespace final : public JS::Object {
+    JS_OBJECT(CSSNamespace, JS::Object)
+
+public:
+    explicit CSSNamespace(JS::GlobalObject&);
+    virtual void initialize(JS::GlobalObject&) override;
+    virtual ~CSSNamespace() override;
+
+private:
+    JS_DECLARE_NATIVE_FUNCTION(escape);
+    JS_DECLARE_NATIVE_FUNCTION(supports);
+};
+
+}

Userland/Libraries/LibWeb/Bindings/WindowObject.cpp

@@ -13,6 +13,7 @@
 #include <LibJS/Runtime/FunctionObject.h>
 #include <LibJS/Runtime/Shape.h>
 #include <LibTextCodec/Decoder.h>
+#include <LibWeb/Bindings/CSSNamespace.h>
 #include <LibWeb/Bindings/CSSStyleDeclarationWrapper.h>
 #include <LibWeb/Bindings/CryptoWrapper.h>
 #include <LibWeb/Bindings/DocumentWrapper.h>
@@ -104,6 +105,8 @@ void WindowObject::initialize_global_object()
     define_native_accessor("screenLeft", screen_left_getter, {}, attr);
     define_native_accessor("screenTop", screen_top_getter, {}, attr);
 
+    define_direct_property("CSS", heap().allocate<CSSNamespace>(*this, *this), 0);
+
     // Legacy
     define_native_accessor("event", event_getter, event_setter, JS::Attribute::Enumerable);