Use std::string references instead of copying contents.

talk/media/webrtc/webrtcvideocapturer.cc

 /*
  * libjingle
  * Copyright 2011 Google Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
  *
  *  1. Redistributions of source code must retain the above copyright notice,
  *     this list of conditions and the following disclaimer.
  *  2. Redistributions in binary form must reproduce the above copyright notice,
@@ skipping 247 matching lines @@
                  << best_format->ToString();
   }
   return true;
 }
 bool WebRtcVideoCapturer::SetApplyRotation(bool enable) {
   // Can't take lock here as this will cause deadlock with
   // OnIncomingCapturedFrame. In fact, the whole method, including methods it
   // calls, can't take lock.
   DCHECK(module_);
 
-  const std::string group_name =
+  const std::string& group_name =
       webrtc::field_trial::FindFullName("WebRTC-CVO");
 
   if (group_name == "Disabled") {
     return true;
   }
 
   if (!VideoCapturer::SetApplyRotation(enable)) {
     return false;
   }
   return module_->SetApplyRotation(enable);
@@ skipping 158 matching lines @@
   elapsed_time = sample.render_time_ms() * rtc::kNumNanosecsPerMillisec;
   time_stamp = elapsed_time;
   data_size = rtc::checked_cast<uint32>(length);
   data = buffer;
   rotation = sample.rotation();
 }
 
 }  // namespace cricket
 
 #endif  // HAVE_WEBRTC_VIDEO