[Offline Pages] Turn Offliner::Cancel into an async operation to resolve conflicting assumptions

chrome/browser/android/offline_pages/prerendering_offliner.h

 // 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.
 
 #ifndef CHROME_BROWSER_ANDROID_OFFLINE_PAGES_PRERENDERING_OFFLINER_H_
 #define CHROME_BROWSER_ANDROID_OFFLINE_PAGES_PRERENDERING_OFFLINER_H_
 
 #include <memory>
 
 #include "base/android/application_status_listener.h"
@@ skipping 18 matching lines @@
 class PrerenderingOffliner : public Offliner {
  public:
   PrerenderingOffliner(content::BrowserContext* browser_context,
                        const OfflinerPolicy* policy,
                        OfflinePageModel* offline_page_model);
   ~PrerenderingOffliner() override;
 
   // Offliner implementation.
   bool LoadAndSave(const SavePageRequest& request,
                    const CompletionCallback& callback) override;
-  void Cancel() override;
+  void Cancel(const CancelCallback& callback) override;
 
   // Allows a loader to be injected for testing. This may only be done once
   // and must be called before any of the Offliner interface methods are called.
   void SetLoaderForTesting(std::unique_ptr<PrerenderingLoader> loader);
 
   void SetLowEndDeviceForTesting(bool is_low_end_device);
 
   void SetApplicationStateForTesting(
       base::android::ApplicationState application_state);
 
@@ skipping 15 matching lines @@
   // Callback logic for OfflinePageModel::SavePage().
   void OnSavePageDone(const SavePageRequest& request,
                       SavePageResult save_result,
                       int64_t offline_id);
 
   PrerenderingLoader* GetOrCreateLoader();
 
   // Listener function for changes to application background/foreground state.
   void OnApplicationStateChange(
       base::android::ApplicationState application_state);
+  void HandleApplicationStateChangeCancel(const SavePageRequest& request,
+                                          int64_t offline_id);
 
   // Not owned.
   content::BrowserContext* browser_context_;
   // Not owned.
   OfflinePageModel* offline_page_model_;
   // Lazily created.
   std::unique_ptr<PrerenderingLoader> loader_;
   // Tracks pending request, if any. Owned copy.
   // May be used to ensure a callback applies to the pending request (e.g., in
   // case we receive a save page callback for an old, canceled request).
   std::unique_ptr<SavePageRequest> pending_request_;
   // Callback to call when pending request completes/fails.
   CompletionCallback completion_callback_;
   bool is_low_end_device_;
   // ApplicationStatusListener to monitor if the Chrome moves to the foreground.
   std::unique_ptr<base::android::ApplicationStatusListener> app_listener_;
   base::WeakPtrFactory<PrerenderingOffliner> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(PrerenderingOffliner);
 };
 
 }  // namespace offline_pages
 
 #endif  // CHROME_BROWSER_ANDROID_OFFLINE_PAGES_PRERENDERING_OFFLINER_H_