Cleanup: Pass std::string as const reference from content/

content/renderer/media/rtc_peer_connection_handler.cc

 // Copyright (c) 2012 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 "content/renderer/media/rtc_peer_connection_handler.h"
 
 #include <string>
 #include <utility>
 #include <vector>
 
@@ skipping 477 matching lines @@
 
   rtc::scoped_refptr<LocalRTCStatsRequest> request_;
   const scoped_refptr<base::SingleThreadTaskRunner> main_thread_;
   base::ThreadChecker signaling_thread_checker_;
 };
 
 void GetStatsOnSignalingThread(
     const scoped_refptr<webrtc::PeerConnectionInterface>& pc,
     webrtc::PeerConnectionInterface::StatsOutputLevel level,
     const scoped_refptr<webrtc::StatsObserver>& observer,
-    const std::string track_id, blink::WebMediaStreamSource::Type track_type) {
+    const std::string& track_id,
+    blink::WebMediaStreamSource::Type track_type) {
   TRACE_EVENT0("webrtc", "GetStatsOnSignalingThread");
 
   scoped_refptr<webrtc::MediaStreamTrackInterface> track;
   if (!track_id.empty()) {
     if (track_type == blink::WebMediaStreamSource::TypeAudio) {
       track = pc->local_streams()->FindAudioTrack(track_id);
       if (!track.get())
         track = pc->remote_streams()->FindAudioTrack(track_id);
     } else {
       DCHECK_EQ(blink::WebMediaStreamSource::TypeVideo, track_type);
@@ skipping 1118 matching lines @@
 }
 
 void RTCPeerConnectionHandler::ResetUMAStats() {
   DCHECK(thread_checker_.CalledOnValidThread());
   num_local_candidates_ipv6_ = 0;
   num_local_candidates_ipv4_ = 0;
   ice_connection_checking_start_ = base::TimeTicks();
   memset(ice_state_seen_, 0, sizeof(ice_state_seen_));
 }
 }  // namespace content