Return a copy of the supported RTP header extensions instead of a reference.

talk/media/webrtc/webrtcvoiceengine_unittest.cc

Index: talk/media/webrtc/webrtcvoiceengine_unittest.cc
diff --git a/talk/media/webrtc/webrtcvoiceengine_unittest.cc b/talk/media/webrtc/webrtcvoiceengine_unittest.cc
index 888de7d8a485e4254a9edaa898efa06edf75a080..61cfe691370aeef73fcc8db1e7a669012b0f21c0 100644
--- a/talk/media/webrtc/webrtcvoiceengine_unittest.cc
+++ b/talk/media/webrtc/webrtcvoiceengine_unittest.cc
@@ -3113,7 +3113,7 @@ TEST_F(WebRtcVoiceEngineTestFake, ConfiguresAudioReceiveStreamRtpExtensions) {
   }
 
   // Set up receive extensions.
-  const auto& e_exts = engine_.rtp_header_extensions();
+  const auto& e_exts = engine_.SupportedRtpHeaderExtensions();
   cricket::AudioRecvParameters recv_parameters;
   recv_parameters.extensions = e_exts;
   channel_->SetRecvParameters(recv_parameters);