1You can just put jquery.js into extension folder and include it in the manifest:
2
3{
4  "name": "My extension",
5  ...
6  "content_scripts": [
7    {
8      "matches": ["http://www.google.com/*"],
9      "css": ["mystyles.css"],
10      "js": ["jquery.js", "myscript.js"]
11    }
12  ],
13  ...
14}
15You don't need to worry about conflicts with jQuery on a parent page as content scripts are sandboxed.

1"content_security_policy": "script-src 'self' https://ajax.googleapis.com; object-src 'self'",
2