Offline Page Cache uses user interaction triggers for saving pages.

chrome/browser/android/offline_pages/recent_tab_helper.h

Index: chrome/browser/android/offline_pages/recent_tab_helper.h
diff --git a/chrome/browser/android/offline_pages/recent_tab_helper.h b/chrome/browser/android/offline_pages/recent_tab_helper.h
index 94c69e4ff1bd586eb30f75bfb41957955e2ebe7a..da26060675de9b0afc90da0dc91382104c3c1636 100644
--- a/chrome/browser/android/offline_pages/recent_tab_helper.h
+++ b/chrome/browser/android/offline_pages/recent_tab_helper.h
@@ -22,6 +22,8 @@ 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
@@ -39,6 +41,7 @@ class RecentTabHelper
   void DocumentAvailableInMainFrame() override;
   void DocumentOnLoadCompletedInMainFrame() override;
   void WebContentsDestroyed() override;
+  void WasHidden() override;
 
   // SnapshotController::Client
   void StartSnapshot() override;
@@ -102,18 +105,20 @@ class RecentTabHelper
   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.
@@ -131,6 +136,16 @@ class RecentTabHelper
 
   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);