Offline Page Cache: do not save a snapshot of a page loaded from a snapshot.

chrome/browser/android/offline_pages/recent_tab_helper.cc

 // Copyright (c) 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.
 
 #include "chrome/browser/android/offline_pages/recent_tab_helper.h"
 
 #include <queue>
 #include <vector>
 
 #include "base/bind.h"
@@ skipping 146 matching lines @@
     download_info_.reset();
   }
 
   is_page_ready_for_snapshot_ = false;
 
   // New navigation, new snapshot session.
   snapshot_url_ = web_contents()->GetLastCommittedURL();
 
   // Check for conditions that would cause us not to snapshot.
   bool can_save = !navigation_handle->IsErrorPage() &&
-                  OfflinePageModel::CanSaveURL(snapshot_url_);
+                  OfflinePageModel::CanSaveURL(snapshot_url_) &&
+                  OfflinePageUtils::GetOfflinePageFromWebContents(
+                      web_contents()) == nullptr;
 
   UMA_HISTOGRAM_BOOLEAN("OfflinePages.CanSaveRecentPage", can_save);
 
   // Always reset so that posted tasks get canceled.
   snapshot_controller_->Reset();
 
   if (!can_save)
     snapshot_controller_->Stop();
 }
 
@@ skipping 109 matching lines @@
 bool RecentTabHelper::IsSamePage() const {
   return web_contents() &&
          (web_contents()->GetLastCommittedURL() == snapshot_url_);
 }
 
 ClientId RecentTabHelper::GetRecentPagesClientId() const {
   return ClientId(kLastNNamespace, tab_id_);
 }
 
 }  // namespace offline_pages