Removing $(document).ready should fix your problem. I tried your code and after commenting out $(document).ready, it worked:

//$(document).load(function() {
    google.load('visualization', '1', {packages:['intensitymap']});
    google.setOnLoadCallback(drawChart);
//});

Now as for why this is the case, I do not know... In any case, you shouldn't need to wait for document.ready to call google.load; google.load will ensure that by the time your callback drawChart is called, it will be safe to execute.