[OfflinePages] RequestCoordinatorFactory return null for incognito

chrome/browser/android/offline_pages/prerendering_offliner_factory.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/android/offline_pages/prerendering_offliner_factory.h"
 
 #include "chrome/browser/android/offline_pages/offline_page_model_factory.h"
 #include "chrome/browser/android/offline_pages/prerendering_offliner.h"
 
 namespace offline_pages {
@@ skipping 16 matching lines @@
   // TODO(petewil): Think about whether there might be any threading
   // issues.  This should always happen on the same thread, but make sure.
 
   // Build a prerendering offliner if we don't already have one cached.
   if (offliner_ == nullptr) {
     // TODO(petewil): Create a PrerenderManager, use for 2nd arg below.
 
     // Get a pointer to the (unowned) offline page model.
     OfflinePageModel* model =
         OfflinePageModelFactory::GetInstance()->GetForBrowserContext(context_);
-
+    // Ensure we do have a model for saving a page if we prerender it.
+    DCHECK(model) << "No OfflinePageModel for offliner";
     offliner_ = new PrerenderingOffliner(context_, policy, model);
   }
 
   return offliner_;
 }
 
 }  // namespace offline_pages