When I use following URL in browser then it prompt me to download a text file with JSOn content.
https://chart.googleapis.com/chart?cht=p3&chs=250x100&chd=t:
Depending on your PHP configuration, this may be a easy as using:
$jsonData = json_decode(file_get_contents('https://chart.googleapis.com/chart?cht=p3&chs=250x100&chd=t:60,40&chl=Hello|World&chof=json'));
However, if allow_url_fopen isn't enabled on your system, you could read the data via CURL as follows:
Incidentally, if you just want the raw JSON data, then simply remove the json_decode.