Coverity: Pass parameters by reference.

chrome/browser/extensions/extension_tts_api.h

 // 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.
 
 #ifndef CHROME_BROWSER_EXTENSIONS_EXTENSION_TTS_API_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_TTS_API_H_
 
 #include <queue>
 #include <string>
 
@@ skipping 130 matching lines @@
   // Speak the given utterance. If the utterance's can_enqueue flag is true
   // and another utterance is in progress, adds it to the end of the queue.
   // Otherwise, interrupts any current utterance and speaks this one
   // immediately.
   void SpeakOrEnqueue(Utterance* utterance);
 
   // Stop all utterances and flush the queue.
   void Stop();
 
   // Called when an extension finishes speaking an utterance.
-  void OnSpeechFinished(int request_id, std::string error_message);
+  void OnSpeechFinished(int request_id, const std::string& error_message);
 
   // For unit testing.
   void SetPlatformImpl(ExtensionTtsPlatformImpl* platform_impl);
 
  private:
   ExtensionTtsController();
   virtual ~ExtensionTtsController();
 
   // Get the platform TTS implementation (or injected mock).
   ExtensionTtsPlatformImpl* GetPlatformImpl();
@@ skipping 65 matching lines @@
 };
 
 class ExtensionTtsSpeakCompletedFunction : public SyncExtensionFunction {
  private:
   ~ExtensionTtsSpeakCompletedFunction() {}
   virtual bool RunImpl();
   DECLARE_EXTENSION_FUNCTION_NAME("experimental.tts.speakCompleted")
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_TTS_API_H_