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;

[dewittj, 2017/01/20 22:41:26]

Does this pollute the namespace? in other words, could someone else refer to
offline_pages::PageQuality?  If so we should not alias this here.

[carlosk, 2017/01/20 23:04:35]

I'm unsure but I agree it's a problem. I'll move this into the .CC and use the
full namespace name here.

+
 // 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 35 matching lines @@
     ClientId client_id;
 
     // Id of the suspended request in Background Offliner. Used to un-suspend
     // the request if the capture of the current page was not possible (e.g.
     // the user navigated to another page before current one was loaded).
     // 0 if this is a "last_n" info.
     int64_t request_id = OfflinePageModel::kInvalidOfflineId;
 
     // True if there was at least one snapshot successfully completed.
     bool page_snapshot_completed = false;
+
+    // Expected snapshot quality should the saving succeed. This value is only
+    // valid if |page_snapshot_completed| is true.
+    PageQuality expected_page_quality = PageQuality::POOR;
   };
 
   explicit RecentTabHelper(content::WebContents* web_contents);
   friend class content::WebContentsUserData<RecentTabHelper>;
 
-  void EnsureInitialized();
-  void ContinueSnapshotWithIdsToPurge(const std::vector<int64_t>& page_ids);
-  void ContinueSnapshotAfterPurge(OfflinePageModel::DeletePageResult result);
-  void SavePageCallback(OfflinePageModel::SavePageResult result,
+  bool EnsureInitialized();
+  void ContinueSnapshotWithIdsToPurge(SnapshotProgressInfo* snapshot_info,
+                                      const std::vector<int64_t>& page_ids);
+  void ContinueSnapshotAfterPurge(SnapshotProgressInfo* snapshot_info,
+                                  OfflinePageModel::DeletePageResult result);
+  void SavePageCallback(SnapshotProgressInfo* snapshot_info,
+                        OfflinePageModel::SavePageResult result,
                         int64_t offline_id);
-  void ReportSnapshotCompleted();
-  void ReportDownloadStatusToRequestCoordinator();
-  bool IsSamePage() const;
+  void ReportSnapshotCompleted(SnapshotProgressInfo* snapshot_info);
+  void ReportDownloadStatusToRequestCoordinator(
+      SnapshotProgressInfo* snapshot_info);
   ClientId GetRecentPagesClientId() const;
+  void SaveSnapshotForDownloads();
 
   // Page model is a service, no ownership. Can be null - for example, in
   // case when tab is in incognito profile.
   OfflinePageModel* page_model_ = nullptr;
 
   // If false, never make snapshots off the attached WebContents.
   // Not page-specific.
   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_ = false;
+  // Snapshot progress information for a downloads triggered request. Null if
+  // downloads is not capturing or hasn't captured the current page.
+  std::unique_ptr<SnapshotProgressInfo> downloads_latest_snapshot_info_;
 
-  // Info for the offline page to capture. Null if the tab is not capturing
-  // current page.
-  std::unique_ptr<SnapshotProgressInfo> snapshot_info_;
+  // Snapshot progress information for a last_n triggered request. Null if
+  // last_n is not currently capturing the current page.
+  std::unique_ptr<SnapshotProgressInfo> last_n_ongoing_snapshot_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.
+
+  // Monitors page loads and starts snapshots when a download request exist. It
+  // is also used as an initialization flag for EnsureInitialized() to be run
+  // only once.
   std::unique_ptr<SnapshotController> snapshot_controller_;
 
   std::unique_ptr<Delegate> delegate_;
 
+  // Set at each navigation to control if last_n should save snapshots of the
+  // current page being loaded.
+  bool last_n_listen_to_tab_hidden_ = false;
+
+  // Track the page quality status of the last saved snapshot for the current
+  // page. It is generally reset upon new navigations.
+  PageQuality last_n_latest_saved_quality_ = 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_