1 files changed, 104 insertions, 0 deletions
diff --git a/browser/components/newtab/content-src/lib/perf-service.js b/browser/components/newtab/content-src/lib/perf-service.js
new file mode 100644
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+++ b/browser/components/newtab/content-src/lib/perf-service.js
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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+let usablePerfObj = window.performance;
+
+export function _PerfService(options) {
+  // For testing, so that we can use a fake Window.performance object with
+  // known state.
+  if (options && options.performanceObj) {
+    this._perf = options.performanceObj;
+  } else {
+    this._perf = usablePerfObj;
+  }
+}
+
+_PerfService.prototype = {
+  /**
+   * Calls the underlying mark() method on the appropriate Window.performance
+   * object to add a mark with the given name to the appropriate performance
+   * timeline.
+   *
+   * @param  {String} name  the name to give the current mark
+   * @return {void}
+   */
+  mark: function mark(str) {
+    this._perf.mark(str);
+  },
+
+  /**
+   * Calls the underlying getEntriesByName on the appropriate Window.performance
+   * object.
+   *
+   * @param  {String} name
+   * @param  {String} type eg "mark"
+   * @return {Array}       Performance* objects
+   */
+  getEntriesByName: function getEntriesByName(name, type) {
+    return this._perf.getEntriesByName(name, type);
+  },
+
+  /**
+   * The timeOrigin property from the appropriate performance object.
+   * Used to ensure that timestamps from the add-on code and the content code
+   * are comparable.
+   *
+   * @note If this is called from a context without a window
+   * (eg a JSM in chrome), it will return the timeOrigin of the XUL hidden
+   * window, which appears to be the first created window (and thus
+   * timeOrigin) in the browser.  Note also, however, there is also a private
+   * hidden window, presumably for private browsing, which appears to be
+   * created dynamically later.  Exactly how/when that shows up needs to be
+   * investigated.
+   *
+   * @return {Number} A double of milliseconds with a precision of 0.5us.
+   */
+  get timeOrigin() {
+    return this._perf.timeOrigin;
+  },
+
+  /**
+   * Returns the "absolute" version of performance.now(), i.e. one that
+   * should ([bug 1401406](https://bugzilla.mozilla.org/show_bug.cgi?id=1401406)
+   * be comparable across both chrome and content.
+   *
+   * @return {Number}
+   */
+  absNow: function absNow() {
+    return this.timeOrigin + this._perf.now();
+  },
+
+  /**
+   * This returns the absolute startTime from the most recent performance.mark()
+   * with the given name.
+   *
+   * @param  {String} name  the name to lookup the start time for
+   *
+   * @return {Number}       the returned start time, as a DOMHighResTimeStamp
+   *
+   * @throws {Error}        "No Marks with the name ..." if none are available
+   *
+   * @note Always surround calls to this by try/catch.  Otherwise your code
+   * may fail when the `privacy.resistFingerprinting` pref is true.  When
+   * this pref is set, all attempts to get marks will likely fail, which will
+   * cause this method to throw.
+   *
+   * See [bug 1369303](https://bugzilla.mozilla.org/show_bug.cgi?id=1369303)
+   * for more info.
+   */
+  getMostRecentAbsMarkStartByName(name) {
+    let entries = this.getEntriesByName(name, "mark");
+
+    if (!entries.length) {
+      throw new Error(`No marks with the name ${name}`);
+    }
+
+    let mostRecentEntry = entries[entries.length - 1];
+    return this._perf.timeOrigin + mostRecentEntry.startTime;
+  },
+};
+
+export const perfService = new _PerfService();