LibJS: Implement most of the Reflect object

Libraries/LibJS/Tests/Reflect.ownKeys.js

@@ -0,0 +1,39 @@
+load("test-common.js");
+
+try {
+    assert(Reflect.ownKeys.length === 1);
+
+    [null, undefined, "foo", 123, NaN, Infinity].forEach(value => {
+        assertThrowsError(() => {
+            Reflect.ownKeys(value);
+        }, {
+            error: TypeError,
+            message: "First argument of Reflect.ownKeys() must be an object"
+        });
+    });
+
+    var objectOwnKeys = Reflect.ownKeys({});
+    assert(objectOwnKeys.length === 0);
+
+    objectOwnKeys = Reflect.ownKeys({ foo: "bar", bar: "baz", 0: 42 });
+    assert(objectOwnKeys.length === 3);
+    assert(objectOwnKeys[0] === "0");
+    assert(objectOwnKeys[1] === "foo");
+    assert(objectOwnKeys[2] === "bar");
+
+    var arrayOwnKeys = Reflect.ownKeys([]);
+    assert(arrayOwnKeys.length === 1);
+    assert(arrayOwnKeys[0] === "length");
+
+    arrayOwnKeys = Reflect.ownKeys(["foo", [], 123, undefined]);
+    assert(arrayOwnKeys.length === 5);
+    assert(arrayOwnKeys[0] === "0");
+    assert(arrayOwnKeys[1] === "1");
+    assert(arrayOwnKeys[2] === "2");
+    assert(arrayOwnKeys[3] === "3");
+    assert(arrayOwnKeys[4] === "length");
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}