Now does not sync URLs that only have imported visits.

chrome/browser/history/history_backend.h

 // Copyright (c) 2011 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_HISTORY_HISTORY_BACKEND_H_
 #define CHROME_BROWSER_HISTORY_HISTORY_BACKEND_H_
 #pragma once
 
 #include <string>
 #include <utility>
@@ skipping 283 matching lines @@
 
   virtual bool UpdateURL(URLID id, const history::URLRow& url);
 
   // While adding visits in batch, the source needs to be provided.
   virtual bool AddVisits(const GURL& url,
                          const std::vector<history::VisitInfo>& visits,
                          VisitSource visit_source);
 
   virtual bool RemoveVisits(const VisitVector& visits);
 
+  virtual bool GetVisitsSource(const VisitVector& visits,

[sky, 2011/10/21 22:44:51]

Does this really need to be virtual?
Add a description too.

[Andrew T Wilson (Slow), 2011/10/22 06:48:22]

Done.

+                               VisitSourceMap* sources);
+
   virtual bool GetURL(const GURL& url, history::URLRow* url_row);
 
   // Deleting ------------------------------------------------------------------
 
   virtual void DeleteURLs(const std::vector<GURL>& urls);
 
   virtual void DeleteURL(const GURL& url);
 
   // Calls ExpireHistoryBackend::ExpireHistoryBetween and commits the change.
   void ExpireHistoryBetween(
@@ skipping 317 matching lines @@
   // Publishes the history to all indexers which are registered to receive
   // history data from us. Can be NULL if there are no listeners.
   scoped_ptr<HistoryPublisher> history_publisher_;
 
   DISALLOW_COPY_AND_ASSIGN(HistoryBackend);
 };
 
 }  // namespace history
 
 #endif  // CHROME_BROWSER_HISTORY_HISTORY_BACKEND_H_