Index: frontend/node_modules/w3c-hr-time/lib/calculate-clock-offset.js
===================================================================
--- frontend/node_modules/w3c-hr-time/lib/calculate-clock-offset.js	(revision 9af201e94b5a79beb92a30858fc54de4bc3b9449)
+++ frontend/node_modules/w3c-hr-time/lib/calculate-clock-offset.js	(revision 9af201e94b5a79beb92a30858fc54de4bc3b9449)
@@ -0,0 +1,39 @@
+"use strict";
+
+// This files implements the calculation of the offset between the global monotonic clock and UNIX time. This value is
+// known as |t1| in the calculation of "time origin timestamp" in the spec. This value needs to be calculated once and
+// can be used in all subsequent Performance instances.
+//
+// However, if the clock is not fast enough, the export is undefined to signify that we should use Date.now() to get the
+// time origin timestamp with millisecond accuracy, per spec.
+
+const { getGlobalMonotonicClockMS } = require("./global-monotonic-clock");
+const clockIsAccurate = require("./clock-is-accurate");
+
+// This function assumes the clock is accurate.
+function calculateClockOffset() {
+  const start = Date.now();
+  let cur = start;
+  // Limit the iterations, just in case we're running in an environment where Date.now() has been mocked and is
+  // constant.
+  for (let i = 0; i < 1e6 && cur === start; i++) {
+    cur = Date.now();
+  }
+
+  // At this point |cur| "just" became equal to the next millisecond -- the unseen digits after |cur| are approximately
+  // all 0, and |cur| is the closest to the actual value of the UNIX time. Now, get the current global monotonic clock
+  // value and do the remaining calculations.
+
+  return cur - getGlobalMonotonicClockMS();
+}
+
+if (clockIsAccurate) {
+  // Warm up the function.
+  calculateClockOffset();
+  calculateClockOffset();
+  calculateClockOffset();
+
+  module.exports = calculateClockOffset;
+} else {
+  module.exports = undefined;
+}
Index: frontend/node_modules/w3c-hr-time/lib/clock-is-accurate.js
===================================================================
--- frontend/node_modules/w3c-hr-time/lib/clock-is-accurate.js	(revision 9af201e94b5a79beb92a30858fc54de4bc3b9449)
+++ frontend/node_modules/w3c-hr-time/lib/clock-is-accurate.js	(revision 9af201e94b5a79beb92a30858fc54de4bc3b9449)
@@ -0,0 +1,61 @@
+"use strict";
+
+const { hrtime } = require("./utils");
+
+// The HR-TIME spec calls for 5-μs accuracy. Check that we have that in both hrtime() and Date.now().
+
+function testClockAccuracy() {
+  // Test hrtime() first. The check is simpler and more stable, and we use hrtime() to measure Date.now()'s performance.
+  const roundTrip = hrtime(hrtime());
+  if (roundTrip[0] > 1 || roundTrip[1] > 5e3 * 2) {
+    return false;
+  }
+
+  // Test Date.now() twice: first with a looser bound (10 μs) but with a smaller run time to filter out very bad
+  // Date.now() performance, and then with a tighter bound (5 μs) to check we have the accuracy we need.
+  let times;
+  // eslint-disable-next-line no-unused-vars
+  let cur;
+  let start;
+  let end;
+
+  times = 100;
+  start = hrtime();
+  while (times-- > 0) {
+    cur = Date.now();
+  }
+  end = hrtime(start);
+  if ((end[0] * 1e9 + end[1]) > 1000000) {
+    return false;
+  }
+
+  times = 10000;
+  start = hrtime();
+  while (times-- > 0) {
+    cur = Date.now();
+  }
+  end = hrtime(start);
+  if ((end[0] * 1e9 + end[1]) > 50000000) {
+    return false;
+  }
+
+  return true;
+}
+
+// Warm up the function.
+testClockAccuracy();
+testClockAccuracy();
+testClockAccuracy();
+
+const TIMES = 5;
+const THRESHOLD = 0.6 * TIMES;
+let accurates = 0;
+for (let i = 0; i < TIMES; i++) {
+  if (testClockAccuracy()) {
+    accurates++;
+  }
+}
+
+const isAccurate = accurates >= THRESHOLD;
+
+module.exports = isAccurate;
Index: frontend/node_modules/w3c-hr-time/lib/global-monotonic-clock.js
===================================================================
--- frontend/node_modules/w3c-hr-time/lib/global-monotonic-clock.js	(revision 9af201e94b5a79beb92a30858fc54de4bc3b9449)
+++ frontend/node_modules/w3c-hr-time/lib/global-monotonic-clock.js	(revision 9af201e94b5a79beb92a30858fc54de4bc3b9449)
@@ -0,0 +1,10 @@
+"use strict";
+
+const { hrtime, toMS } = require("./utils");
+
+// Returns the DOMHighResTimeStamp representing the high resolution time value of the global monotonic clock.
+function getGlobalMonotonicClockMS() {
+  return toMS(hrtime());
+}
+
+module.exports = { getGlobalMonotonicClockMS };
Index: frontend/node_modules/w3c-hr-time/lib/performance.js
===================================================================
--- frontend/node_modules/w3c-hr-time/lib/performance.js	(revision 9af201e94b5a79beb92a30858fc54de4bc3b9449)
+++ frontend/node_modules/w3c-hr-time/lib/performance.js	(revision 9af201e94b5a79beb92a30858fc54de4bc3b9449)
@@ -0,0 +1,53 @@
+"use strict";
+
+// Actual implementation of the Performance class.
+
+const clockIsAccurate = require("./clock-is-accurate");
+const calculateClockOffset = require("./calculate-clock-offset");
+const { hrtime, toMS } = require("./utils");
+
+const kTimeOrigin = Symbol("time origin");
+const kTimeOriginTimestamp = Symbol("time origin timestamp");
+
+class Performance {
+  constructor() {
+    // Time origin.
+    const timeOrigin = hrtime();
+    this[kTimeOrigin] = timeOrigin;
+
+    if (clockIsAccurate) {
+      // Let |t1| be the DOMHighResTimeStamp representing the high resolution Unix time at which the global monotonic
+      // clock is zero. This has to be calculated for every Performance object to account for clock drifts.
+      const t1 = calculateClockOffset();
+
+      // Let |t2| be the DOMHighResTimeStamp representing the high resolution time value of the global monotonic clock
+      // at global's time origin.
+      const t2 = toMS(timeOrigin);
+
+      // Return the sum of |t1| and |t2|.
+      this[kTimeOriginTimestamp] = t1 + t2;
+    } else {
+      // Clock isn't accurate enough. Use millisecond accuracy per spec.
+      const cur = Date.now();
+      this[kTimeOriginTimestamp] = cur;
+    }
+  }
+
+  // The timeOrigin getter actually returns the time origin timestamp, not the raw time origin.
+  get timeOrigin() {
+    return this[kTimeOriginTimestamp];
+  }
+
+  now() {
+    const diff = toMS(hrtime(this[kTimeOrigin]));
+    return clockIsAccurate ? diff : Math.round(diff);
+  }
+
+  toJSON() {
+    return {
+      timeOrigin: this.timeOrigin
+    };
+  }
+}
+
+module.exports = { Performance };
Index: frontend/node_modules/w3c-hr-time/lib/utils.js
===================================================================
--- frontend/node_modules/w3c-hr-time/lib/utils.js	(revision 9af201e94b5a79beb92a30858fc54de4bc3b9449)
+++ frontend/node_modules/w3c-hr-time/lib/utils.js	(revision 9af201e94b5a79beb92a30858fc54de4bc3b9449)
@@ -0,0 +1,11 @@
+"use strict";
+
+// Browserify's process implementation doesn't have hrtime, and this package is small so not much of a burden for
+// Node.js users.
+const hrtime = require("browser-process-hrtime");
+
+function toMS([sec, nanosec]) {
+  return sec * 1e3 + nanosec / 1e6;
+}
+
+module.exports = { hrtime, toMS };