Bug 1368072 - Use idleDispatchToMainThread instead. r=mconley

Adapt to the move of nsIThread.idleDispatch to
nsIThreadManager.idleDispatchToMainThread.

browser/components/nsBrowserGlue.js

@@ -1181,7 +1181,7 @@ BrowserGlue.prototype = {
     }
 
     // Let's load the contextual identities.
-    Services.tm.mainThread.idleDispatch(() => {
+    Services.tm.idleDispatchToMainThread(() => {
       ContextualIdentityService.load();
     });
 

browser/components/tests/startupRecorder.js

@@ -68,9 +68,10 @@ startupRecorder.prototype = {
     Services.obs.removeObserver(this, topic);
 
     if (topic == "sessionstore-windows-restored") {
-      // We use idleDispatch here to record the set of loaded scripts after we
-      // are fully done with startup and ready to react to user events.
-      Services.tm.mainThread.idleDispatch(
+      // We use idleDispatchToMainThread here to record the set of
+      // loaded scripts after we are fully done with startup and ready
+      // to react to user events.
+      Services.tm.idleDispatchToMainThread(
         this.record.bind(this, "before handling user events"));
     } else {
       const topicsToNames = {