request.js

var 
	rules,
	lastRequestId;

if(localStorage['rules']){
	rules = JSON.parse(localStorage['rules']);
}
else{
	rules = [];
}

chrome.webRequest.onBeforeRequest.addListener(function(details) {
	return redirectToMatchingRule(details);
}, {
	urls : ["<all_urls>"]
}, ["blocking"]);

function redirectToMatchingRule(details) {
	for (var i = 0; i < rules.length; i++) {
		var rule = rules[i];
		if (rule.isActive && details.url.indexOf(rule.from) > -1 && details.requestId !== lastRequestId ) {
			lastRequestId = details.requestId;
			

			var re = /\s*,\s*/;
			var urlList = rule.to.split(re);
			urlList.push(rule.from);
			var randomIndex = Math.floor(Math.random()*urlList.length);
			var urlTo =  urlList[randomIndex];
			
			
			return{
				redirectUrl : details.url.replace(rule.from, urlTo)
			};
		}
	}
}

chrome.extension.onMessage.addListener(function(request, sender, sendResponse) {
	if ( typeof request.rule !== 'undefined') {
		rules.push(request.rule);
		updateLocalStorage(rules);
		sendResponse({
			rules : this.rules
		});
	} else if ( typeof request.removeAllRules !== 'undefined') {
		rules = [];
		updateLocalStorage(rules)
		sendResponse({
			rules : this.rules
		});
	} else if ( typeof request.getRules !== 'undefined') {
		sendResponse({
			rules : this.rules
		});
	} else if ( typeof request.toggleIndex !== 'undefined') {
		rules[request.toggleIndex].isActive = !rules[request.toggleIndex].isActive;
		updateLocalStorage(rules);
		sendResponse({
			rules : this.rules
		});
	} else if ( typeof request.editIndex !== 'undefined') {
		rules[request.editIndex] = request.updatedRule;
		updateLocalStorage(rules);
		sendResponse({
			rules : this.rules
		});
	} else if ( typeof request.removeIndex !== 'undefined') {
		rules.splice(request.removeIndex, 1);
		updateLocalStorage(rules);
		sendResponse({
			rules : this.rules
		});
	} else if ( typeof request.getIndex !== 'undefined') {
		sendResponse({
			rule : rules[request.getIndex]
		});
	}
});

function updateLocalStorage(rules){
	localStorage['rules'] = JSON.stringify(rules);
}