Error Message:

Error: GoogleChartsController Compile Error: Incompatible types since an instance of ApexPages.StandardController is never an instance of Account at line 5 column 15

Controller:

global class GoogleChartsController {
 global static Account acc;
 
    public GoogleChartsController(ApexPages.StandardController controller) {
        acc = (Account)controller.getRecord();
    }
@RemoteAction   
    global static AggregateResult[] loadChildCases(Id prmAccountId) {
        AggregateResult[] caseLst = [Select ParentId, count(Id) FROM Case  WHERE AccountId = :prmAccountId Group By ParentId ];
        
        return caseLst;
    }
    }

VF Page:

<apex:page extensions="GoogleChartsController" sidebar="false" standardController="Account" showHeader="false" pageStyle="Account"  >
    <apex:includeScript id="a" value="https://www.google.com/jsapi" />     
    <script type="text/javascript">
        // Load the Visualization API and the piechart package.
        google.load('visualization', '1.0', {'packages':['corechart']});
        // Set a callback to run when the Google Visualization API is loaded.
        google.setOnLoadCallback(initCharts);
        //load all the charts..
        function initCharts() {
              GoogleChartsController.loadChildCases('{!acc.Id}', function(resultCase, event){  
                  var visualization = new google.visualization.ColumnChart(document.getElementById('caseChart'));
                  var data1 = new google.visualization.DataTable();  
                  data1.addColumn('string', 'Cases');
                  data1.addColumn('number', 'Cases');       
                  //add rows from the remoting results
                  for(var i =0; i < resultCase.length; i++){
                      var r = resultCase[i];
                      data1.addRow([r.Id, r.expr0]);
                   }
                    // all done, lets draw the chart with some options to make it look nice.
                    visualization.draw(data1, {legend : {position: 'top', textStyle: {color: 'blue', fontSize: 10}}, width:150,vAxis:{textStyle:{fontSize: 10}},hAxis:{textStyle:{fontSize: 10},showTextEvery:1,slantedText:false}});
              }, {escape:true});
              
          }
    </script>
     <div id="caseChart" />
</apex:page>