Bug 1545879 - Port bug 1520321 and bug 1544562: Changes to Application Updater. r=jorgk

Bug 1520321 - Implement XPCOM interface for interacting with the update agent.
Bug 1544562 - aboutDialog-appUpdater's onUnload doesn't run in about:preferences

mail/app/profile/all-thunderbird.js

@@ -117,6 +117,11 @@ pref("app.update.idletime", 60);
 pref("app.update.service.enabled", true);
 #endif
 
+#ifdef XP_WIN
+// This pref prevents BITS from being used by Thunderbird to download updates.
+pref("app.update.BITS.enabled", false);
+#endif
+
 // Release notes URL
 pref("app.releaseNotesURL", "https://live.thunderbird.net/%APP%/releasenotes?locale=%LOCALE%&version=%VERSION%&channel=%CHANNEL%&os=%OS%&buildid=%APPBUILDID%");
 

mail/base/content/aboutDialog-appUpdater.js

@@ -18,11 +18,13 @@ const PREF_APP_UPDATE_ELEVATE_NEVER    = "app.update.elevate.never";
 var gAppUpdater;
 
 function onUnload(aEvent) {
-  if (gAppUpdater.isChecking)
-    gAppUpdater.checker.stopCurrentCheck();
-  // Safe to call even when there isn't a download in progress.
-  gAppUpdater.removeDownloadListener();
-  gAppUpdater = null;
+  if (gAppUpdater) {
+    if (gAppUpdater.isChecking)
+      gAppUpdater.checker.stopCurrentCheck();
+    // Safe to call even when there isn't a download in progress.
+    gAppUpdater.removeDownloadListener();
+    gAppUpdater = null;
+  }
 }
 
 
@@ -294,7 +296,6 @@ appUpdater.prototype = {
     this.update.QueryInterface(Ci.nsIWritablePropertyBag);
     this.update.setProperty("foregroundDownload", "true");
 
-    this.aus.pauseDownload();
     let state = this.aus.downloadUpdate(this.update, false);
     if (state == "failed") {
       this.selectPanel("downloadFailed");

mail/components/preferences/advanced.js

@@ -785,6 +785,9 @@ var gAdvancedPane = {
   handleEvent(aEvent) {
     if (aEvent.type == "unload") {
       this.destroy();
+      if (AppConstants.MOZ_UPDATER) {
+        onUnload();
+      }
     }
   },