Fix android -Wshorten-64-to-32 error: https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket.appspot.com/8844689770192651952/+/u/compile__with_patch_/raw_io.output_failure_summary_

The compiler option is not added to default_copts because it breaks too many other quic and spdy code. This fix only makes the chromium bot green.

PiperOrigin-RevId: 379252123

quic/core/quic_stream.h

diff --git a/quic/core/quic_stream.h b/quic/core/quic_stream.h
index ca20eb4..51080cd 100644
--- a/quic/core/quic_stream.h
+++ b/quic/core/quic_stream.h
@@ -478,7 +478,7 @@
     explicit MemSliceSpanWrapper(absl::Span<QuicMemSlice> span) : new_(span) {}
 
     bool empty() { return old_.has_value() ? old_->empty() : new_.empty(); }
-    size_t SaveTo(QuicStreamSendBuffer& send_buffer) {
+    QuicByteCount SaveTo(QuicStreamSendBuffer& send_buffer) {
       if (old_.has_value()) {
         return send_buffer.SaveMemSliceSpan(*old_);
       }