Add option to attach custom object to an rtp packet

As an alternative to attaching custom array of bytes.

Bug: b/178094662
Change-Id: I92dcbf04998d8206091125febc520ebfcc4bcebf
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/203264
Reviewed-by: Christoffer Rodbro <crodbro@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Emil Lundmark <lndmrk@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33069}
diff --git a/api/BUILD.gn b/api/BUILD.gn
index 3c73d51..0cb6490 100644
--- a/api/BUILD.gn
+++ b/api/BUILD.gn
@@ -575,6 +575,10 @@
     "call/transport.cc",
     "call/transport.h",
   ]
+  deps = [
+    ":refcountedbase",
+    ":scoped_refptr",
+  ]
 }
 
 rtc_source_set("bitrate_allocation") {