Movable support for VideoReceiveStream::Config and avoid copies

webrtc/video_receive_stream.h

Index: webrtc/video_receive_stream.h
diff --git a/webrtc/video_receive_stream.h b/webrtc/video_receive_stream.h
index 167df47dff4cc052471500f5f4600f7856cfed67..896676bc111911c9c5a96e3bb7ba9b859a46a361 100644
--- a/webrtc/video_receive_stream.h
+++ b/webrtc/video_receive_stream.h
@@ -76,10 +76,23 @@ class VideoReceiveStream {
   };
 
   struct Config {
+   private:
+    // Access to the copy constructor is private to force use of the Copy()
+    // method for those exceptional cases where we do use it.
+    Config(const Config&) = default;
+
+   public:
     Config() = delete;
+    Config(Config&&) = default;
     explicit Config(Transport* rtcp_send_transport)
         : rtcp_send_transport(rtcp_send_transport) {}
 
+    Config& operator=(Config&&) = default;
+    Config& operator=(const Config&) = delete;
+
+    // Mostly used by tests.  Avoid creating copies if you can.
+    Config Copy() const { return Config(*this); }
+
     std::string ToString() const;
 
     // Decoders for every payload that we can receive.