HistoryService: clarify documentation about QueryRedirectsCallback behavior.

chrome/browser/history/history_service.h

 // Copyright (c) 2012 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_SERVICE_H_
 #define CHROME_BROWSER_HISTORY_HISTORY_SERVICE_H_
 
 #include <set>
 #include <vector>
 
@@ skipping 256 matching lines @@
   // Queries all history with the given options (see QueryOptions in
   // history_types.h).  If empty, all results matching the given options
   // will be returned.
   Handle QueryHistory(const base::string16& text_query,
                       const history::QueryOptions& options,
                       CancelableRequestConsumerBase* consumer,
                       const QueryHistoryCallback& callback);
 
   // Called when the results of QueryRedirectsFrom are available.
   // The given vector will contain a list of all redirects, not counting
-  // the original page. If A redirects to B, the vector will contain only B,
-  // and A will be in 'source_url'.
+  // the original page. If A redirects to B which redirects to C, the vector
+  // will contain [B, C], and A will be in 'from_url'.
+  //
+  // For QueryRedirectsTo, the order is reversed. For A->B->C, the vector will
+  // contain [B, A] and C will be in 'to_url'.
   //
   // If there is no such URL in the database or the most recent visit has no
   // redirect, the vector will be empty. If the history system failed for
   // some reason, success will additionally be false. If the given page
   // has redirected to multiple destinations, this will pick a random one.
   typedef base::Callback<void(Handle,
-                              GURL,  // from_url
+                              GURL,  // from_url / to_url
                               bool,  // success
                               history::RedirectList*)> QueryRedirectsCallback;
 
   // Schedules a query for the most recent redirect coming out of the given
   // URL. See the RedirectQuerySource above, which is guaranteed to be called
   // if the request is not canceled.
   Handle QueryRedirectsFrom(const GURL& from_url,
                             CancelableRequestConsumerBase* consumer,
                             const QueryRedirectsCallback& callback);
 
@@ skipping 768 matching lines @@
   scoped_ptr<history::InMemoryURLIndex> in_memory_url_index_;
 
   ObserverList<history::VisitDatabaseObserver> visit_database_observers_;
 
   history::DeleteDirectiveHandler delete_directive_handler_;
 
   DISALLOW_COPY_AND_ASSIGN(HistoryService);
 };
 
 #endif  // CHROME_BROWSER_HISTORY_HISTORY_SERVICE_H_