[Offline Pages] Moves Coordinator to using MarkAttemptStarted/MarkAttemptCompleted API.

chrome/browser/android/offline_pages/prerendering_offliner.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.h"
 
 #include "base/bind.h"
 #include "base/sys_info.h"
 #include "chrome/browser/android/offline_pages/offline_page_mhtml_archiver.h"
 #include "components/offline_pages/background/save_page_request.h"
@@ skipping 89 matching lines @@
   } else {
     // TODO(dougarnett): Consider reflecting some recommendation to retry the
     // request based on specific save error cases.
     save_status = RequestStatus::SAVE_FAILED;
   }
   completion_callback_.Run(request, save_status);
 }
 
 bool PrerenderingOffliner::LoadAndSave(const SavePageRequest& request,
                                        const CompletionCallback& callback) {
+  DCHECK(!pending_request_.get());
+
   if (pending_request_) {
     DVLOG(1) << "Already have pending request";
     return false;
   }
 
   if (!GetOrCreateLoader()->CanPrerender()) {
     DVLOG(1) << "Prerendering not allowed/configured";
     return false;
   }
 
@@ skipping 70 matching lines @@
           base::android::APPLICATION_STATE_HAS_RUNNING_ACTIVITIES) {
     DVLOG(1) << "App became active, canceling current offlining request";
     SavePageRequest* request = pending_request_.get();
     Cancel();
     completion_callback_.Run(*request,
                              Offliner::RequestStatus::FOREGROUND_CANCELED);
   }
 }
 
 }  // namespace offline_pages