How we can create google chart from apex class in Salesforce?

<apex:page >
<apex:includeScript id="a" value="https://www.google.com/jsapi" />
<apex:sectionHeader subtitle="Reactive Call Outs Per Day"/>
<!-- Google Charts will be drawn in this DIV -->
<div id="chart_div" />

<script type="text/javascript" src="/soap/ajax/20.0/connection.js?x74638"></script>
<script type="text/javascript">
sforce.connection.sessionId = "{!$Api.Session_ID}";
var result = sforce.connection.query("SELECT DAY_ONLY(CreatedDate) days, count(createdDate) counts FROM Visits__c where createdDate = LAST_N_Days:90 GROUP BY DAY_ONLY(CreatedDate) order by DAY_ONLY(createdDate) desc");
records = result.getArray("records");
// Load the Visualization API and the piechart package.
google.load('visualization', '1.0', {'packages':['corechart']});
google.setOnLoadCallback(drawCharts);
function drawCharts() {
var data = new google.visualization.DataTable();
data.addColumn('string', 'Created Date');
data.addColumn('number', 'Record Count');
data.addRows(records.length);
for(var i = 0 ; i < records.length ; i++){
data.setValue(i,0,records[i].days);
data.setValue(i,1,records[i].counts);
}
var options = {
title: '',
hAxis: {title: 'days'},
vAxis: {title: 'counts'},
legend: 'none',
trendlines: { 0: {color: 'red',} } // Draw a trendline for data series 0.
};
var visualization = new google.visualization.ColumnChart(document.getElementById('chart_div'));
visualization.draw(data,options);
}
</script>
</apex:page>