Coverity: Pass parameters by reference.

chrome/browser/extensions/extension_tts_api.cc

 // 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.
 
 #include <string>
 #include <vector>
 
 #include "base/float_util.h"
 #include "base/json/json_writer.h"
 #include "base/message_loop.h"
@@ skipping 239 matching lines @@
     GetPlatformImpl()->StopSpeaking();
   }
 
   if (current_utterance_)
     current_utterance_->set_error(kSpeechInterruptedError);
   FinishCurrentUtterance();
   ClearUtteranceQueue();
 }
 
 void ExtensionTtsController::OnSpeechFinished(
-    int request_id, std::string error_message) {
+    int request_id, const std::string& error_message) {
   // We may sometimes receive completion callbacks "late", after we've
   // already finished the utterance (for example because another utterance
   // interrupted or we got a call to Stop). It's also possible that a buggy
   // extension has called this more than once. In either case it's safe to
   // just ignore this call.
   if (!current_utterance_ || request_id != current_utterance_->id())
     return;
 
   current_utterance_->set_error(error_message);
   FinishCurrentUtterance();
@@ skipping 106 matching lines @@
   int request_id;
   std::string error_message;
   EXTENSION_FUNCTION_VALIDATE(args_->GetInteger(0, &request_id));
   if (args_->GetSize() >= 2)
     EXTENSION_FUNCTION_VALIDATE(args_->GetString(1, &error_message));
   ExtensionTtsController::GetInstance()->OnSpeechFinished(
       request_id, error_message);
 
   return true;
 }