// background.html
// ---------------------
<script src="sample.js"></script>

// sample.js
// ---------------------
var localS = 0;
chrome.extension.onRequest.addListener(function(request, sender, sendResponse) {
    if (request.count>0){
		localS=request.count;
		sendResponse({msg: "thanks"});
	}
    else
		sendResponse({});
});

// contentscript.js
// ---------------------
var c = localStorage["engine_count"];
chrome.extension.sendRequest({count: [c]}, function(response) {
  console.log(response.msg);
});