Last_n: do not delete the currently loading offline snapshot.

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>
 
@@ skipping 115 matching lines @@
   // This is set to true if the ongoing snapshot for downloads is waiting on the
   // page to reach a minimal quality level to start.
   bool downloads_snapshot_on_hold_ = false;
 
   // Snapshot information for the last successful snapshot requested by
   // downloads. Null if no successful one has ever completed for the current
   // page.
   std::unique_ptr<SnapshotProgressInfo> downloads_latest_saved_snapshot_info_;
 
   // Snapshot progress information for a last_n triggered request. Null if
-  // last_n is not currently capturing the current page.
+  // last_n is not currently capturing the current page. It is cleared upon non
+  // ignored navigations.
   std::unique_ptr<SnapshotProgressInfo> last_n_ongoing_snapshot_info_;
 
   // Snapshot information for the last successful snapshot requested by
   // last_n. Null if no successful one has ever completed for the current page.
+  // It is cleared when the referenced snapshot is deleted.
   std::unique_ptr<SnapshotProgressInfo> last_n_latest_saved_snapshot_info_;
 
   // If empty, the tab does not have AndroidId and can not capture pages.
   std::string tab_id_;
 
   // 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;
 
   // Set to true when the tab containing the associated WebContents is in the
   // process of being closed.
   bool tab_is_closing_ = false;
 
   base::WeakPtrFactory<RecentTabHelper> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RecentTabHelper);
 };
 
 }  // namespace offline_pages
 
 #endif  // CHROME_BROWSER_ANDROID_OFFLINE_PAGES_RECENT_TAB_HELPER_H_