Add support for editing the logfile headers

This lets us fix bugs in logfiles if the need arises.

Change-Id: I374c4f6b3745835af2279d4b29f6f8098a5d7770
diff --git a/aos/events/logging/logfile_utils.h b/aos/events/logging/logfile_utils.h
index 6b8e9aa..5b2bfa6 100644
--- a/aos/events/logging/logfile_utils.h
+++ b/aos/events/logging/logfile_utils.h
@@ -44,6 +44,8 @@
   void QueueSizedFlatbuffer(flatbuffers::FlatBufferBuilder *fbb);
   // Queues up a detached buffer directly.
   void QueueSizedFlatbuffer(flatbuffers::DetachedBuffer &&buffer);
+  // Writes a Span.  This is not terribly optimized right now.
+  void WriteSizedFlatbuffer(absl::Span<const uint8_t> span);
 
   // Triggers data to be provided to the kernel and written.
   void Flush();