// inject.js
// runs when page URL changes
chrome.extension.onMessage.addListener(function(msg, sender, sendResponse) {
	if (msg.action == 'tab_updated') {
		// do stuff
	}
});

// background.js
chrome.tabs.onUpdated.addListener(function listener(tabId, changedProps) {
	if (changedProps.status != "complete") {
		return;
	}
	chrome.tabs.query({active: true}, function(tabs) {		
		chrome.tabs.sendMessage(tabs[0].id, {action: "tab_updated"}, function(response) { });
	});
});