When including external hosted javascript files, you need to specify that it is external
when calling the drupal_add_js
function. When not specifying this argument, Drupal will try to load it on the file system (which doesn't exists).
drupal_add_js('https://www.google.com/jsapi', 'external');
Update
It seems that you are experiencing the blank page problem. Could you try with the following javascript code, I've changed the callback definition passing it directly through the load function.
google.load("visualization", "1", { 'callback': 'drawChart', packages: ["corechart"] });
function drawChart() {
var data = google.visualization.arrayToDataTable([
['Task', 'Hours per Day'],
['Work', 1],
['Eat', 2],
['Commute', 2],
['Watch TV', 2],
['Sleep', 7]
]);
var options = {
title: 'My Daily Activities',
pieHole: 0.4
};
var chart = new google.visualization.PieChart(document.getElementById('donutchart'));
chart.draw(data, options);
}