Scripting.createTestWindow(): take params

Take a parameter object rather than a long parameter list containing
multiple booleans.

https://bugzilla.gnome.org/show_bug.cgi?id=732349

js/perf/core.js

@@ -87,7 +87,10 @@ function run() {
             yield Scripting.destroyTestWindows();
 
             for (let k = 0; k < config.count; k++)
-                yield Scripting.createTestWindow(config.width, config.height, config.alpha, config.maximized);
+                yield Scripting.createTestWindow({ width: config.width,
+                                                   height: config.height,
+                                                   alpha: config.alpha,
+                                                   maximized: config.maximized });
 
             yield Scripting.waitTestWindows();
             yield Scripting.sleep(1000);