Coverity: Fix pass-by-value.

chrome/common/net/gaia/oauth2_mint_token_fetcher.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/common/net/gaia/oauth2_mint_token_fetcher.h"
 
 #include <algorithm>
 #include <string>
 
 #include "base/json/json_reader.h"
@@ skipping 119 matching lines @@
   std::string access_token;
   ParseMintTokenResponse(source, &access_token);
   OnMintTokenSuccess(access_token);
 }
 
 void OAuth2MintTokenFetcher::OnMintTokenSuccess(
     const std::string& access_token) {
   consumer_->OnMintTokenSuccess(access_token);
 }
 
-void OAuth2MintTokenFetcher::OnMintTokenFailure(GoogleServiceAuthError error) {
+void OAuth2MintTokenFetcher::OnMintTokenFailure(
+    const GoogleServiceAuthError& error) {
   state_ = ERROR_STATE;
   consumer_->OnMintTokenFailure(error);
 }
 
 void OAuth2MintTokenFetcher::OnURLFetchComplete(const URLFetcher* source) {
   CHECK(source);
   CHECK_EQ(MINT_TOKEN_STARTED, state_);
   EndMintToken(source);
 }
 
@@ skipping 29 matching lines @@
   std::string data;
   source->GetResponseAsString(&data);
   base::JSONReader reader;
   scoped_ptr<base::Value> value(reader.Read(data, false));
   if (!value.get() || value->GetType() != base::Value::TYPE_DICTIONARY)
     return false;
 
   DictionaryValue* dict = static_cast<DictionaryValue*>(value.get());
   return dict->GetString(kAccessTokenKey, access_token);
 }