ResourceTiming leak to parent frames

resourcetiming-iframe.js

//
// Placed in any cross-origin IFRAMEs
//
if (window !== window.top) {
    if (typeof window.PerformanceObserver !== "function") {
        return;
    }

    // Listen for all ResourceTimings, repeating them to the parent window
    var observer = new PerformanceObserver(function(entries) {
        window.top.postMessage({
            type: "resourcetiming",
            entries: JSON.stringify(entries.getEntries()),
            origin: window.performance.timeOrigin || window.performance.timing.navigationStart
        }, "*");
    });

    observer.observe({entryTypes: ['resource']});

    // repeat any sub-frame's ResourceTiming data
    window.addEventListener("message", function(event) {
        if (event.data && event.data.type === "resourcetiming") {
            window.top.postMessage(event.data, "*");
        }
    }, false);
}

resourcetiming-parent.js

//
// Placed in the top-level window
//

// list of all ResourceTimings from cross-origin IFRAMEs
var iframeEntries = [];

window.addEventListener("message", function(event) {
    if (event.data && event.data.type === "resourcetiming") {
        // RT entries are JSON.stringify'd
        var entries = JSON.parse(event.data.entries);
        var myOrigin = window.performance.timeOrigin || window.performance.timing.navigationStart;
        var offsetTime = event.data.origin - myOrigin;

        // update each entry's startTime by the offset of the two frame's time origins
        for (var i = 0; i < entries.length; i++) {
            entries[i].startTime += offsetTime;
        }

        Array.prototype.push.apply(iframeEntries, entries);
    }
}, false);