Bug 513944 - Weave should not load / do anything until it absolutely needs to

Weave already triggers on a late notification and puts itself on the event loop, so just additionally delay startup based on the number of open tabs (which will all be busy at startup).

services/sync/Weave.js

@@ -62,7 +62,7 @@ WeaveService.prototype = {
     */
     case "sessionstore-windows-restored":
       Cu.import("resource://weave/service.js");
-      Weave.Utils.delay(function() Weave.Service.onStartup());
+      Weave.Service.onStartup();
       break;
     }
   }

services/sync/modules/service.js

@@ -303,14 +303,36 @@ WeaveSvc.prototype = {
   onWindowOpened: function WeaveSvc__onWindowOpened() {
   },
 
+  /**
+   * Prepare to initialize the rest of Weave after waiting a little bit
+   */
+  onStartup: function onStartup() {
+    this._status = new StatusRecord();
+    this.status.service = STATUS_DELAYED;
+
+    // Figure out how many seconds to delay loading Weave based on the app
+    let wait = 0;
+    switch (Svc.AppInfo.ID) {
+      case FIREFOX_ID:
+        // Add one second delay for each tab in every window
+        let enum = Svc.WinMediator.getEnumerator("navigator:browser");
+        while (enum.hasMoreElements())
+          wait += enum.getNext().gBrowser.mTabs.length;
+    }
+
+    // Make sure we wait a little but but not too long in the worst case
+    wait = Math.ceil(Math.max(5, Math.min(20, wait)));
+
+    this._initLogs();
+    this._log.info("Loading Weave " + WEAVE_VERSION + " in " + wait + " sec.");
+    Utils.delay(this._onStartup, wait * 1000, this, "_startupTimer");
+  },
+
   // one-time initialization like setting up observers and the like
   // xxx we might need to split some of this out into something we can call
   //     again when username/server/etc changes
-  onStartup: function WeaveSvc_onStartup() {
-    this._initLogs();
-    this._log.info("Weave " + WEAVE_VERSION + " initializing");
+  _onStartup: function _onStartup() {
     this._registerEngines();
-    this._status = new StatusRecord();
 
     // Reset our sync id if we're upgrading, so sync knows to reset local data
     if (WEAVE_VERSION != Svc.Prefs.get("lastversion")) {