Add expect_final_byte_offset argument to CopyAndValidateTrailers().

This will be used in cr/231494986 where trailers sent on the
request/response stream should not have the :final-offset pseudo-header.

gfe-relnote: n/a.  No functional change.
PiperOrigin-RevId: 243730777
Change-Id: I1a5c729fb5aab3e3abdb0ce64dad5667faf794bf
diff --git a/quic/core/http/quic_spdy_stream.cc b/quic/core/http/quic_spdy_stream.cc
index fd77668..674b076 100644
--- a/quic/core/http/quic_spdy_stream.cc
+++ b/quic/core/http/quic_spdy_stream.cc
@@ -449,7 +449,9 @@
   }
 
   size_t final_byte_offset = 0;
-  if (!SpdyUtils::CopyAndValidateTrailers(header_list, &final_byte_offset,
+  if (!SpdyUtils::CopyAndValidateTrailers(header_list,
+                                          /* expect_final_byte_offset = */ true,
+                                          &final_byte_offset,
                                           &received_trailers_)) {
     QUIC_DLOG(ERROR) << "Trailers for stream " << id() << " are malformed.";
     session()->connection()->CloseConnection(