[Coverity] Fix pass-by-val to pass-by-ref

chrome/common/net/gaia/oauth_request_signer.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/common/net/gaia/oauth_request_signer.h"
 
 #include <cctype>
 #include <cstddef>
 #include <cstdlib>
 #include <cstring>
@@ skipping 60 matching lines @@
       return "RSA-SHA1";
     case OAuthRequestSigner::PLAINTEXT_SIGNATURE:
       return "PLAINTEXT";
   }
   NOTREACHED();
   return *(new std::string());
 }
 
 std::string BuildBaseString(const GURL& request_base_url,
                             OAuthRequestSigner::HttpMethod http_method,
-                            const std::string base_parameters) {
+                            const std::string& base_parameters) {
   return StringPrintf("%s&%s&%s",
                       HttpMethodName(http_method).c_str(),
                       OAuthRequestSigner::Encode(
                           request_base_url.spec()).c_str(),
                       OAuthRequestSigner::Encode(
                           base_parameters).c_str());
 }
 
 std::string BuildBaseStringParameters(
     const OAuthRequestSigner::Parameters& parameters) {
@@ skipping 357 matching lines @@
         signed_text += ", ";
       signed_text +=
           StringPrintf("%s=\"%s\"",
                        OAuthRequestSigner::Encode(param->first).c_str(),
                        OAuthRequestSigner::Encode(param->second).c_str());
     }
     *signed_text_return = signed_text;
   }
   return is_signed;
 }