Let SessionDescription take ownership of MediaDescription

This documents in the API what is already true in the
implementation - that SessionDescription will eventually
delete MediaDescription objects passed to it.

The old API is preserved for backwards compatibility, but
marked as RTC_DEPRECATED.

Bug: webrtc:10701
Change-Id: I9a822b20cf3e58c5945fa51dbf6082960a332de8
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/139880
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Steve Anton <steveanton@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28144}
diff --git a/pc/jsep_transport_controller_unittest.cc b/pc/jsep_transport_controller_unittest.cc
index d796b23..3bde0e7 100644
--- a/pc/jsep_transport_controller_unittest.cc
+++ b/pc/jsep_transport_controller_unittest.cc
@@ -146,7 +146,7 @@
     // Set RTCP-mux to be true because the default policy is "mux required".
     audio->set_rtcp_mux(true);
     description->AddContent(mid, cricket::MediaProtocolType::kRtp,
-                            /*rejected=*/false, audio.release());
+                            /*rejected=*/false, std::move(audio));
     AddTransportInfo(description, mid, ufrag, pwd, ice_mode, conn_role, cert);
   }
 
@@ -162,7 +162,7 @@
     // Set RTCP-mux to be true because the default policy is "mux required".
     video->set_rtcp_mux(true);
     description->AddContent(mid, cricket::MediaProtocolType::kRtp,
-                            /*rejected=*/false, video.release());
+                            /*rejected=*/false, std::move(video));
     AddTransportInfo(description, mid, ufrag, pwd, ice_mode, conn_role, cert);
   }
 
@@ -179,7 +179,7 @@
         new cricket::SctpDataContentDescription());
     data->set_rtcp_mux(true);
     description->AddContent(mid, protocol_type,
-                            /*rejected=*/false, data.release());
+                            /*rejected=*/false, std::move(data));
     AddTransportInfo(description, mid, ufrag, pwd, ice_mode, conn_role, cert);
   }