Offline Page Cache uses user interaction triggers for saving pages.

chrome/browser/android/offline_pages/recent_tab_helper.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_RECENT_TAB_HELPER_H_
 #define CHROME_BROWSER_ANDROID_OFFLINE_PAGES_RECENT_TAB_HELPER_H_
 
 #include <memory>
 #include <vector>
 
 #include "base/memory/weak_ptr.h"
 #include "components/offline_pages/core/downloads/download_ui_item.h"
 #include "components/offline_pages/core/offline_page_model.h"
 #include "components/offline_pages/core/snapshot_controller.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "content/public/browser/web_contents_user_data.h"
 #include "url/gurl.h"
 
 namespace content {
 class NavigationHandle;
 }
 
 namespace offline_pages {
 
+using PageQuality = SnapshotController::PageQuality;
+
 // Attaches to every WebContent shown in a tab. Waits until the WebContent is
 // loaded to proper degree and then makes a snapshot of the page. Removes the
 // oldest snapshot in the 'ring buffer'. As a result, there is always up to N
 // snapshots of recent pages on the device.
 class RecentTabHelper
     : public content::WebContentsObserver,
       public content::WebContentsUserData<RecentTabHelper>,
       public SnapshotController::Client {
  public:
   ~RecentTabHelper() override;
 
   // content::WebContentsObserver
   void DidFinishNavigation(
       content::NavigationHandle* navigation_handle) override;
   void DocumentAvailableInMainFrame() override;
   void DocumentOnLoadCompletedInMainFrame() override;
   void WebContentsDestroyed() override;
+  void WasHidden() override;
 
   // SnapshotController::Client
   void StartSnapshot() override;
 
   // Delegate that is used by RecentTabHelper to get external dependencies.
   // Default implementation lives in .cc file, while tests provide an override.
   class Delegate {
    public:
     virtual ~Delegate() {}
     virtual std::unique_ptr<OfflinePageArchiver> CreatePageArchiver(
@@ skipping 43 matching lines @@
 
   void EnsureInitialized();
   void ContinueSnapshotWithIdsToPurge(const std::vector<int64_t>& page_ids);
   void ContinueSnapshotAfterPurge(OfflinePageModel::DeletePageResult result);
   void SavePageCallback(OfflinePageModel::SavePageResult result,
                         int64_t offline_id);
   void ReportSnapshotCompleted();
   void ReportDownloadStatusToRequestCoordinator();
   bool IsSamePage() const;
   ClientId GetRecentPagesClientId() const;
+  void StartSnapshotInternal();
+  bool isSnapshottingForLastN() const;
 
   // Page model is a service, no ownership. Can be null - for example, in
   // case when tab is in incognito profile.
-  OfflinePageModel* page_model_;
+  OfflinePageModel* page_model_ = nullptr;
 
   // If false, never make snapshots off the attached WebContents.
   // Not page-specific.
-  bool snapshots_enabled_;
+  bool snapshots_enabled_ = false;
 
   // Becomes true during navigation if the page is ready for snapshot as
   // indicated by at least one callback from SnapshotController.
-  bool is_page_ready_for_snapshot_;
+  bool is_page_ready_for_snapshot_ = false;
 
   // Info for the offline page to capture. Null if the tab is not capturing
   // current page.
   std::unique_ptr<DownloadPageInfo> download_info_;
 
   // If empty, the tab does not have AndroidId and can not capture pages.
   std::string tab_id_;
 
   // The URL of the page that is currently being snapshotted. Used to check,
   // during async operations, that WebContents still contains the same page.
   GURL snapshot_url_;
   // This starts out null and used as a flag for EnsureInitialized() to do the
   // initialization only once.
   std::unique_ptr<SnapshotController> snapshot_controller_;
 
   std::unique_ptr<Delegate> delegate_;
 
+  // Per navigation state set if last_n should listed to the tab being hidden to
+  // save a snapshot. Only used if using user interaction events as triggers.
+  bool last_n_listen_to_tab_hidden_ = false;
+
+  // Members to track page quality status for a current save being executed and
+  // the last saved page. Only used if using user interaction events as
+  // triggers.
+  PageQuality last_n_saved_quality_ = PageQuality::POOR;
+  PageQuality page_quality_on_save_start_ = PageQuality::POOR;
+
   base::WeakPtrFactory<RecentTabHelper> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RecentTabHelper);
 };
 
 }  // namespace offline_pages
 #endif  // CHROME_BROWSER_ANDROID_OFFLINE_PAGES_RECENT_TAB_HELPER_H_