Remove all ReadingList entries on managed account signout.

ios/chrome/browser/reading_list/reading_list_download_service.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 "ios/chrome/browser/reading_list/reading_list_download_service.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/files/file_enumerator.h"
@@ skipping 94 matching lines @@
   ProcessNewEntry(url);
 }
 
 void ReadingListDownloadService::ReadingListDidMoveEntry(
     const ReadingListModel* model,
     const GURL& url) {
   DCHECK_EQ(reading_list_model_, model);
   ProcessNewEntry(url);
 }
 
+void ReadingListDownloadService::Clear() {
+  distiller_page_factory_->ReleaseAllRetainedWebState();
+}
+
 void ReadingListDownloadService::ProcessNewEntry(const GURL& url) {
   const ReadingListEntry* entry = reading_list_model_->GetEntryByURL(url);
   if (!entry || entry->IsRead()) {
     url_downloader_->CancelDownloadOfflineURL(url);
   } else {
     ScheduleDownloadEntry(url);
   }
 }
 
 void ReadingListDownloadService::SyncWithModel() {
@@ skipping 172 matching lines @@
     for (auto& url : url_to_download_cellular_) {
       ScheduleDownloadEntry(url);
     }
   }
   if (type == net::NetworkChangeNotifier::CONNECTION_WIFI) {
     for (auto& url : url_to_download_wifi_) {
       ScheduleDownloadEntry(url);
     }
   }
 }