WordPress load jquery from CDN

gistfile1.txt

<?php

class jQuery_CDN {
	/**
	 * @var int
	 */
	private $jquery_version = 0;
	/**
	 * @var int
	 */
	private $jquery_url = null;


	private $already_run = false;

	/**
	 *
	 */
	function __construct() {
		if ( is_admin() ) {
			return;
		}


		add_action( 'wp_enqueue_scripts', array( $this, 'action_wp_enqueue_scripts' ), 100 );
		add_filter( 'script_loader_tag', array( $this, 'filter_script_loader_src' ), 100, 2 );
	}

	function action_wp_enqueue_scripts() {
		global $wp_scripts;


		$this->setJqueryVersion( $wp_scripts->registered['jquery-core']->ver );
		$this->setJqueryUrl( site_url( $wp_scripts->registered['jquery-core']->src ) );
		$jquery_version = $this->getJqueryVersion();

		wp_deregister_script( 'jquery' );

		wp_register_script(
			'jquery',
			'//ajax.googleapis.com/ajax/libs/jquery/' . $jquery_version . '/jquery.min.js',
			array(),
			$jquery_version,
			true
		);


	}

	/**
	 * Output the local fallback immediately after jQuery's <script>
	 *
	 * @link http://wordpress.stackexchange.com/a/12450
	 */
	function filter_script_loader_src( $src, $handle = null ) {

		if ( $handle !== 'jquery' ) {
			return $src;
		}

		if ( $this->isAlreadyRun() ) {
			return $src;
		}

		$src .= '<script>window.jQuery || document.write(\'<script src="' . $this->getJqueryUrl() . '"><\/script>\')</script>' . "\n";

		$this->setAlreadyRun( true );

		return $src;
	}

	/**
	 * @return int
	 */
	public function getJqueryUrl() {
		return $this->jquery_url;
	}

	/**
	 * @param int $jquery_url
	 */
	public function setJqueryUrl( $jquery_url ) {
		$this->jquery_url = $jquery_url;
	}

	/**
	 * @return int
	 */
	public function getJqueryVersion() {
		return $this->jquery_version;
	}

	/**
	 * @param int $jquery_version
	 */
	public function setJqueryVersion( $jquery_version ) {
		$this->jquery_version = $jquery_version;
	}

	/**
	 * @return boolean
	 */
	public function isAlreadyRun() {
		return $this->already_run;
	}

	/**
	 * @param boolean $already_run
	 */
	public function setAlreadyRun( $already_run ) {
		$this->already_run = $already_run;
	}


}

$test = new jQuery_CDN();