Last_n: Do not save a snapshot of a closing tab.

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 50a3cda30a7d4b05c1d01307e0f37ae044768461..6c43a23be1961e0fbd1973a66e7ba5354585e074 100644
--- a/chrome/browser/android/offline_pages/recent_tab_helper.h
+++ b/chrome/browser/android/offline_pages/recent_tab_helper.h
@@ -40,6 +40,11 @@ class RecentTabHelper
   void DocumentOnLoadCompletedInMainFrame() override;
   void WebContentsDestroyed() override;
   void WasHidden() override;
+  void WasShown() override;
+
+  // Notifies that the tab of the associated WebContents will (most probably) be
+  // closed. This call is expected to always happen before the one to WasHidden.
+  void WillCloseTab();
 
   // SnapshotController::Client
   void StartSnapshot() override;
@@ -144,6 +149,10 @@ class RecentTabHelper
   // 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);