Fix #2332, fix #2333: toggle webextension on pref change

Other changes:

* Fix #2370, unset deviceId pref set by old addon.

* Update Promise rejection / Error handling to match behavior
  documented in the addons-related Gecko code.

addon/bootstrap.js

@@ -1,38 +1,104 @@
-/* globals Components, AddonManager */
-/* eslint-disable no-unused-vars */
+/* globals AddonManager, Components, Services */
 
 const OLD_ADDON_PREF_NAME = "extensions.jid1-NeEaf3sAHdKHPA@jetpack.deviceIdInfo";
 const OLD_ADDON_ID = "jid1-NeEaf3sAHdKHPA@jetpack";
+const ADDON_ID = "pageshot@mozilla.org";
+const TELEMETRY_PREF = "toolkit.telemetry.enabled";
+const PREF_BRANCH = "extensions.pageshot.";
+const USER_DISABLE_PREF = "disabled";
+const SYSTEM_DISABLE_PREF = "system-disabled";
 
-const prefs = Components.classes["@mozilla.org/preferences-service;1"]
-  .getService(Components.interfaces.nsIPrefBranch);
-Components.utils.import("resource://gre/modules/AddonManager.jsm");
+const { interfaces: Ci, utils: Cu } = Components;
+Cu.import("resource://gre/modules/AddonManager.jsm");
+Cu.import("resource://gre/modules/Console.jsm");
+Cu.import("resource://gre/modules/Services.jsm");
+const { EmbeddedExtensionManager } = Cu.import("resource://gre/modules/LegacyExtensionsUtils.jsm");
 
-function startup(data, reason) {
-  data.webExtension.startup().then((api) => {
-    const {browser} = api;
-    browser.runtime.onMessage.addListener(handleMessage);
+const prefs = Services.prefs;
+
+function getBoolPref(pref) {
+  return prefs.getPrefType(pref) && prefs.getBoolPref(pref);
+}
+
+function isDisabled() {
+  return getBoolPref(PREF_BRANCH + USER_DISABLE_PREF) ||
+         getBoolPref(PREF_BRANCH + SYSTEM_DISABLE_PREF);
+}
+
+function startup(data, reason) { // eslint-disable-line no-unused-vars
+  handleStartup();
+}
+
+function handleStartup() {
+  AddonManager.getAddonByID(ADDON_ID).then((addon) => {
+    if (addon === null) {
+      console.error('Unable to start WebExtension: wrapper addon not found');
+      return;
+    }
+    const webExtension = EmbeddedExtensionManager.getEmbeddedExtensionFor({
+      id: ADDON_ID,
+      resourceURI: addon.getResourceURI().QueryInterface(Ci.nsIFileURL)
+    });
+
+    if (!isDisabled() && !webExtension.started) {
+      webExtension.startup().then((api) => {
+        api.browser.runtime.onMessage.addListener(handleMessage);
+      }).catch((err) => {
+        // The startup() promise will be rejected if the webExtension was
+        // already started (a harmless error), or if initializing the
+        // WebExtension failed and threw (an important error).
+        console.error(err);
+        if (err.message !== "This embedded extension has already been started") {
+          // TODO: send to sentry? 
+        }
+      });
+    } else if (isDisabled()) {
+      webExtension.shutdown().then(() => {
+        EmbeddedExtensionManager.untrackEmbeddedExtension(webExtension);
+      });
+    }
   });
 }
 
-function shutdown(data, reason) {}
-function install(data, reason) {}
-function uninstall(data, reason) {}
+function shutdown(data, reason) {} // eslint-disable-line no-unused-vars
+function install(data, reason) {} // eslint-disable-line no-unused-vars
+function uninstall(data, reason) {} // eslint-disable-line no-unused-vars
 
 function handleMessage(msg, sender, sendReply) {
   if (msg && msg.funcName === "getTelemetryPref") {
-    let enableTelemetry = prefs.getPrefType('toolkit.telemetry.enabled') && prefs.getBoolPref("toolkit.telemetry.enabled");
+    let enableTelemetry = getBoolPref(TELEMETRY_PREF);
     sendReply({type: "success", value: enableTelemetry});
   } else if (msg && msg.funcName === "getOldDeviceInfo") {
     let oldDeviceInfo = prefs.prefHasUserValue(OLD_ADDON_PREF_NAME) && prefs.getCharPref(OLD_ADDON_PREF_NAME);
     sendReply({type: "success", value: oldDeviceInfo || null});
   } else if (msg && msg.funcName === "removeOldAddon") {
     AddonManager.getAddonByID(OLD_ADDON_ID, (addon) => {
-      // FIXME: remove OLD_ADDON_PREF_NAME, see #2370
+      prefs.clearUserPref(OLD_ADDON_PREF_NAME);
       if (addon) {
         addon.uninstall();
       }
       sendReply({type: "success", value: !! addon});
     });
   }
 }
+
+const pageshotPrefObserver = {
+  register: function() {
+    this.branch = Services.prefs.getBranch("extensions.pageshot.");
+    this.branch.addObserver("", this, false);
+  },
+
+  unregister: function() {
+    this.branch.removeObserver("", this);
+  },
+
+  observe: function(aSubject, aTopic, aData) {
+    // aSubject is the nsIPrefBranch we're observing (after appropriate QI)
+    // aData is the name of the pref that's been changed (relative to aSubject)
+    if (aData == USER_DISABLE_PREF || aData == SYSTEM_DISABLE_PREF) {
+      handleStartup();
+    }
+  }
+};
+
+pageshotPrefObserver.register();