Cleanup: Pass std::string as const reference if possible

chrome/browser/speech/tts_controller_impl.cc

 // Copyright 2014 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/speech/tts_controller_impl.h"
 
 #include <string>
 #include <vector>
 
 #include "base/values.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/speech/tts_platform.h"
 
 namespace {
 // A value to be used to indicate that there is no char index available.
 const int kInvalidCharIndex = -1;
 
 // Given a language/region code of the form 'fr-FR', returns just the basic
 // language portion, e.g. 'fr'.
-std::string TrimLanguageCode(std::string lang) {
+std::string TrimLanguageCode(const std::string& lang) {
   if (lang.size() >= 5 && lang[2] == '-')
     return lang.substr(0, 2);
   else
     return lang;
 }
 
 }  // namespace
 
 bool IsFinalTtsEventType(TtsEventType event_type) {
   return (event_type == TTS_EVENT_END ||
@@ skipping 450 matching lines @@
 }
 
 void TtsControllerImpl::SetTtsEngineDelegate(
     TtsEngineDelegate* delegate) {
   tts_engine_delegate_ = delegate;
 }
 
 TtsEngineDelegate* TtsControllerImpl::GetTtsEngineDelegate() {
   return tts_engine_delegate_;
 }