Chrome onUnload event not triggering

Question

I have set something in local storage (where tabId is the id of the triggering tab [onUpdated event])

var visited = {};
visited[tabId] = true;
chrome.storage.local.set(visited);

I then wish to change the stored variable to false when the page unloads (which I gather happens on refresh, moving to a new webpage or closing the tab)

window.onunload = resetStorage;

function resetStorage() {

    var visited = {};

    chrome.tabs.query({ currentWindow: true }, function (result) {
        result.forEach(function (tab) {
            visited[tab.id] = false;
            console.log(visited);
            chrome.storage.local.set(visited);
        });
    });
};

But this doesn't seem to be triggering (I can't get a console.log to come out, not sure if you can on an unload event?) as it does not change the stored values.

What am I doing wrong?

As some background I am keeping track of whether I have already run code on a page so that it doesn't trigger multiple times from iframe loading or redirections (I think I need additional code to handle redirects).