Change return type of QuicSession::stream_map_size() to fix Chrome build.

No behavior change. not protected.

PiperOrigin-RevId: 324831200
Change-Id: I06038f80852e500c9922b9a1a16627ce7e126d53

quic/core/quic_session.h

diff --git a/quic/core/quic_session.h b/quic/core/quic_session.h
index a49726e..57b95eb 100644
--- a/quic/core/quic_session.h
+++ b/quic/core/quic_session.h
@@ -565,7 +565,7 @@
   StreamMap& stream_map() { return stream_map_; }
 
   // TODO(b/136274541): remove this getter and only expose GetNumActiveStreams()
-  QuicStreamCount stream_map_size() const { return stream_map_.size(); }
+  size_t stream_map_size() const { return stream_map_.size(); }
 
   const PendingStreamMap& pending_streams() const {
     return pending_stream_map_;