Add wallpaper experimental api framework and add a simple category list.

chrome/browser/resources/chromeos/wallpaper_manager/js/main.js

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/**
+ * Global wallpaperManager reference useful for poking at from the console.

[flackr, 2012/07/12 19:40:51]

I don't think it's common to include useful debugging code in commits, is it?

+ */
+var wallpaperManager;
+
+function init() {
+  WallpaperManager.initStrings(function() {
+    wallpaperManager = new WallpaperManager(document.body);
+  });
+}
+
+document.addEventListener('DOMContentLoaded', init);