performance.now() and performance.timing.navigationStart polyfill

performance.now.polyfill.js

// performance.now() and performance.timing.navigationStart polyfill
if (!window.performance) {
    window.performance = {};
}

if (!performance.now) {
    performance.now = function () {
        return Date.now() - this.timing.navigationStart;
    }
}

if (!performance.timing) {
    performance.timing = {};
}

if (!performance.timing.navigationStart) {
    performance.timing.navigationStart = Date.now();
};