Make Symbol() comply with the spec

* Add test of `Symbol()` with multiple arguments.
* Make `Symbol()` comply with the spec. Specifically, it's handling of the second argument to the constructor.

Author: aardvark179

rhino/src/main/java/org/mozilla/javascript/NativeSymbol.java

@@ -90,15 +90,12 @@ private static NativeSymbol getSelf(Scriptable thisObj) {
 
     private static SymbolKey js_constructorCall(
             Context cx, Scriptable scope, Scriptable thisObj, Object[] args) {
-        String desc = null;
+        String desc;
         if (args.length > 0 && !Undefined.isUndefined(args[0])) {
             desc = ScriptRuntime.toString(args[0]);
+        } else {
+            desc = null;
         }
-
-        if (args.length > 1) {
-            return (SymbolKey) args[1];
-        }
-
         return new SymbolKey(desc, Symbol.Kind.REGULAR);
     }
 

tests/testsrc/jstests/es6/symbols.js

@@ -50,6 +50,7 @@ function TestNew() {
       symbols.push(Symbol())
       symbols.push(Symbol(undefined))
       symbols.push(Symbol("66"))
+      symbols.push(Symbol(undefined, "ignored"))
       symbols.push(Symbol(66))
       symbols.push(Symbol().valueOf())
       symbols.push(indirect())