Generally, each data point requires (x,y) coordinates for the chart, but assuming a) you have successfully fetched the data from the file and b) you can get by with just incrementing the 'x' values for each point, you could try something like this:
function drawChart () {
// assumes "file" has the contents of the data file
var dataArray = file.split('\n');
var data = new google.visualization.DataTable();
data.addColumn('number', 'X');
data.addColumn('number', 'Y');
for (var i = 0; i < dataArray.length; i++) {
data.addRow([i, dataArray[i]]);
}
// create and draw chart