Bug 1249845 - bootstrap.js code to manage the e10s staged rollout. r=Mossop

This code decides on a per-branch basis the proportion of users to be part of the e10s rollout, and sets the pref browser.tabs.remote.autostart.2 to true for users part of the test group. It also sets a name for the assigned group to be stored in the telemetry environment.

browser/extensions/e10srollout/bootstrap.js

@@ -0,0 +1,107 @@
+/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*- */
+/* 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/. */
+
+const {classes: Cc, interfaces: Ci, utils: Cu} = Components;
+
+Cu.import("resource://gre/modules/Preferences.jsm");
+Cu.import("resource://gre/modules/UpdateUtils.jsm");
+
+ // The amount of people to be part of e10s, in %
+const TEST_THRESHOLD = {
+  "beta"    : 50,
+  "release" : 0,
+};
+
+const PREF_COHORT_SAMPLE       = "e10s.rollout.cohortSample";
+const PREF_COHORT_NAME         = "e10s.rollout.cohort";
+const PREF_E10S_OPTED_IN       = "browser.tabs.remote.autostart";
+const PREF_E10S_FORCE_ENABLED  = "browser.tabs.remote.force-enable";
+const PREF_E10S_FORCE_DISABLED = "browser.tabs.remote.force-disable";
+const PREF_TOGGLE_E10S         = "browser.tabs.remote.autostart.2";
+
+
+function startup() {
+  // In theory we only need to run this once (on install()), but
+  // it's better to also run it on every startup. If the user has
+  // made manual changes to the prefs, this will keep the data
+  // reported more accurate.
+  // It's also fine (and preferred) to just do it here on startup
+  // (instead of observing prefs), because e10s takes a restart
+  // to take effect, so we keep the data based on how it was when
+  // the session started.
+  defineCohort();
+}
+
+function install() {
+  defineCohort();
+}
+
+let cohortDefinedOnThisSession = false;
+
+function defineCohort() {
+  // Avoid running twice when it was called by install() first
+  if (cohortDefinedOnThisSession) {
+    return;
+  }
+  cohortDefinedOnThisSession = true;
+
+  let updateChannel = UpdateUtils.getUpdateChannel(false);
+  if (!(updateChannel in TEST_THRESHOLD)) {
+    setCohort("unsupportedChannel");
+    return;
+  }
+
+  let userOptedOut = optedOut();
+  let userOptedIn = optedIn();
+  let testGroup = (getUserSample() < TEST_THRESHOLD[updateChannel]);
+
+  if (userOptedOut) {
+    setCohort("optedOut");
+  } else if (userOptedIn) {
+    setCohort("optedIn");
+  } else if (testGroup) {
+    setCohort("test");
+    Preferences.set(PREF_TOGGLE_E10S, true);
+  } else {
+    setCohort("control");
+    Preferences.reset(PREF_TOGGLE_E10S);
+  }
+}
+
+function shutdown(data, reason) {
+}
+
+function uninstall() {
+}
+
+function getUserSample() {
+  let existingVal = Preferences.get(PREF_COHORT_SAMPLE, undefined);
+  if (typeof(existingVal) == "number") {
+    return existingVal;
+  }
+
+  let val = Math.floor(Math.random() * 100);
+  Preferences.set(PREF_COHORT_SAMPLE, val);
+  return val;
+}
+
+function setCohort(cohortName) {
+  Preferences.set(PREF_COHORT_NAME, cohortName);
+}
+
+function optedIn() {
+  return Preferences.get(PREF_E10S_OPTED_IN, false) ||
+         Preferences.get(PREF_E10S_FORCE_ENABLED, false);
+}
+
+function optedOut() {
+  // Users can also opt-out by toggling back the pref to false.
+  // If they reset the pref instead they might be re-enabled if
+  // they are still part of the threshold.
+  return Preferences.get(PREF_E10S_FORCE_DISABLED, false) ||
+         (Preferences.isSet(PREF_TOGGLE_E10S) &&
+          Preferences.get(PREF_TOGGLE_E10S) == false);
+}
+