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

chrome/browser/android/offline_pages/prerendering_offliner.cc

Index: chrome/browser/android/offline_pages/prerendering_offliner.cc
diff --git a/chrome/browser/android/offline_pages/prerendering_offliner.cc b/chrome/browser/android/offline_pages/prerendering_offliner.cc
index 9579bed9e40a19695119b1f96f88eedcdde481f1..e86f3cb259272620693d3820df243bc53733abd3 100644
--- a/chrome/browser/android/offline_pages/prerendering_offliner.cc
+++ b/chrome/browser/android/offline_pages/prerendering_offliner.cc
@@ -107,6 +107,8 @@ void PrerenderingOffliner::OnSavePageDone(
 
 bool PrerenderingOffliner::LoadAndSave(const SavePageRequest& request,
                                        const CompletionCallback& callback) {
+  DCHECK(!pending_request_.get());
+
   if (pending_request_) {
     DVLOG(1) << "Already have pending request";
     return false;