fix spelling of comments

chrome/browser/history/expire_history_backend.h

 // Copyright (c) 2010 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_EXPIRE_HISTORY_BACKEND_H_
 #define CHROME_BROWSER_HISTORY_EXPIRE_HISTORY_BACKEND_H_
 #pragma once
 
 #include <queue>
 #include <set>
@@ skipping 150 matching lines @@
   // database will not be affected (the URL will have to be deleted later).
   //
   // Assumes the archived database is not NULL.
   URLID ArchiveOneURL(const URLRow& url_row);
 
   // Deletes all the URLs in the given vector and handles their dependencies.
   // This will delete starred URLs
   void DeleteURLs(const std::vector<URLRow>& urls,
                   DeleteDependencies* dependencies);
 
-  // Expiration involves removing visits, then propogating the visits out from
+  // Expiration involves removing visits, then propagating the visits out from
   // there and delete any orphaned URLs. These will be added to the deleted URLs
   // field of the dependencies and DeleteOneURL will handle deleting out from
   // there. This function does not handle favicons.
   //
   // When a URL is not deleted and |archive| is not set, the last visit time and
   // the visit and typed counts will be updated (we want to clear these when a
   // user is deleting history manually, but not when we're normally expiring old
   // things from history).
   //
   // The visits in the given vector should have already been deleted from the
@@ skipping 101 matching lines @@
   // Use GetBookmarkService to access this, which makes sure the service is
   // loaded.
   BookmarkService* bookmark_service_;
 
   DISALLOW_COPY_AND_ASSIGN(ExpireHistoryBackend);
 };
 
 }  // namespace history
 
 #endif  // CHROME_BROWSER_HISTORY_EXPIRE_HISTORY_BACKEND_H_