[Spellcheck, OSX] Fix crash

chrome/browser/spellchecker/spelling_service_client.cc

 // 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.
 
 #include "chrome/browser/spellchecker/spelling_service_client.h"
 
 #include "base/command_line.h"
 #include "base/json/json_reader.h"
 #include "base/json/string_escape.h"
 #include "base/logging.h"
@@ skipping 236 matching lines @@
   scoped_ptr<const net::URLFetcher> fetcher(source);
   scoped_ptr<TextCheckCallbackData>
       callback_data(spellcheck_fetchers_[fetcher.get()]);
   bool success = false;
   std::vector<SpellCheckResult> results;
   if (fetcher->GetResponseCode() / 100 == 2) {
     std::string data;
     fetcher->GetResponseAsString(&data);
     success = ParseResponse(data, &results);
   }
+  spellcheck_fetchers_.erase(fetcher.get());
+
+  // The callback may release the last (transitive) dependency on |this|. It
+  // MUST be the last function called.
   callback_data->callback.Run(success, callback_data->text, results);
-  spellcheck_fetchers_.erase(fetcher.get());
 }
 
 net::URLFetcher* SpellingServiceClient::CreateURLFetcher(const GURL& url) {
   return net::URLFetcher::Create(url, net::URLFetcher::POST, this);
 }