Fix a type casting bug in quic stream sequencer buffer.

net/quic/stream_sequencer_buffer.cc

Index: net/quic/stream_sequencer_buffer.cc
diff --git a/net/quic/stream_sequencer_buffer.cc b/net/quic/stream_sequencer_buffer.cc
index 5b98452d03cb8c5425220674b41cd038c2a6a0c7..0582fd70f4dbe5b00f68e1eef8d594d2bf6481e4 100644
--- a/net/quic/stream_sequencer_buffer.cc
+++ b/net/quic/stream_sequencer_buffer.cc
@@ -166,7 +166,7 @@ inline void StreamSequencerBuffer::UpdateGapList(
                  start_offset + bytes_written) {
     // New data has been written into the middle of the buffer.
     auto current = gap_with_new_data_written++;
-    size_t current_end = current->end_offset;
+    QuicStreamOffset current_end = current->end_offset;
     current->end_offset = start_offset;
     gaps_.insert(gap_with_new_data_written,
                  Gap(start_offset + bytes_written, current_end));