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

content/renderer/media/webrtc/media_stream_track_metrics_unittest.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 "base/bind.h"
 #include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/threading/thread.h"
 #include "content/renderer/media/webrtc/media_stream_track_metrics.h"
 #include "content/renderer/media/webrtc/mock_peer_connection_dependency_factory.h"
@@ skipping 114 matching lines @@
     run_loop.Run();
   }
 
   // Convenience methods to cast the mock track types into their webrtc
   // equivalents.
   void AddAudioTrack(AudioTrackInterface* track) { AddTrack(track); }
   void RemoveAudioTrack(AudioTrackInterface* track) { RemoveTrack(track); }
   void AddVideoTrack(VideoTrackInterface* track) { AddTrack(track); }
   void RemoveVideoTrack(VideoTrackInterface* track) { RemoveTrack(track); }
 
-  scoped_refptr<MockAudioTrackInterface> MakeAudioTrack(std::string id) {
+  scoped_refptr<MockAudioTrackInterface> MakeAudioTrack(const std::string& id) {
     return new rtc::RefCountedObject<MockAudioTrackInterface>(id);
   }
 
-  scoped_refptr<MockVideoTrackInterface> MakeVideoTrack(std::string id) {
+  scoped_refptr<MockVideoTrackInterface> MakeVideoTrack(const std::string& id) {
     return new rtc::RefCountedObject<MockVideoTrackInterface>(id);
   }
 
   scoped_ptr<MockMediaStreamTrackMetrics> metrics_;
   scoped_refptr<MediaStreamInterface> stream_;
 
   base::MessageLoopForUI message_loop_;
   base::Thread signaling_thread_;
 };
 
@@ skipping 431 matching lines @@
                                   MediaStreamTrackMetrics::SENT_STREAM));
   EXPECT_CALL(*metrics_,
               SendLifetimeMessage("video3",
                                   MediaStreamTrackMetrics::VIDEO_TRACK,
                                   MediaStreamTrackMetrics::DISCONNECTED,
                                   MediaStreamTrackMetrics::SENT_STREAM));
   metrics_->RemoveStream(MediaStreamTrackMetrics::SENT_STREAM, stream_.get());
 }
 
 }  // namespace content