Now does not sync URLs that only have imported visits.

chrome/browser/history/history_backend.cc

 // 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.
 
 #include "chrome/browser/history/history_backend.h"
 
 #include <list>
 #include <map>
 #include <set>
 #include <vector>
@@ skipping 982 matching lines @@
 
 bool HistoryBackend::RemoveVisits(const VisitVector& visits) {
   if (!db_.get())
     return false;
 
   expirer_.ExpireVisits(visits);
   ScheduleCommit();
   return true;
 }
 
+bool HistoryBackend::GetVisitsSource(const VisitVector& visits,
+                                     VisitSourceMap* sources) {
+  if (!db_.get())
+    return false;
+
+  db_->GetVisitsSource(visits, sources);
+  return true;
+}
+
 bool HistoryBackend::GetURL(const GURL& url, history::URLRow* url_row) {
   if (db_.get())
     return db_->GetRowForURL(url, url_row) != 0;
   return false;
 }
 
 void HistoryBackend::QueryURL(scoped_refptr<QueryURLRequest> request,
                               const GURL& url,
                               bool want_visits) {
   if (request->canceled())
@@ skipping 1277 matching lines @@
         break;
       }
     }
   }
   UMA_HISTOGRAM_TIMES("History.GetFavIconFromDB",  // historical name
                       TimeTicks::Now() - beginning_time);
   return success;
 }
 
 }  // namespace history