Add color enhancer as a chromium accessibility extensions.

ui/accessibility/extensions/colorenhancer/src/common.js

+// Copyright 2015 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.
+
+// TODO(wnwen): Move most of these functions to their own page rather than
+//     common, which should be shared with content script.
+
+/**
+ * TODO(wnwen): Remove this and use actual web API.
+ */
+function $(id) {
+  return document.getElementById(id);
+}
+
+
+/**
+ * TODO(wnwen): Remove this, it's terrible.
+ */
+function siteFromUrl(url) {
+  var a = document.createElement('a');
+  a.href = url;
+  return a.hostname;
+}
+
+
+/**
+ * The filter should not apply to these URLs.
+ *
+ * @param {string} url The URL to check.
+ */
+function isDisallowedUrl(url) {
+  return url.indexOf('chrome') == 0 || url.indexOf('about') == 0;
+}
+
+
+/**
+ * Whether extension is loaded unpacked or from Chrome Webstore.
+ */
+function isDevMode = function() {
+  return !('update_url' in chrome.runtime.getManifest());
+}
+
+
+/**
+ * Easily turn on/off console logs.
+ *
+ * @param {*} message The message to potentially pass to {@code console.log}.
+ */
+var debugPrint;
+if (isDevMode()) {
+  debugPrint = console.log;
+} else {
+  debugPrint = function() {};
+}