Strip data contents out in logfile_utils prints under VLOG(2)

This helps us enormously in keeping the log volume down when there are
large messages in a log file.  The contents are hard to read and not
likely interesting.

Change-Id: I8ee4265a1dd156b2c577db6a4c5f92e43dbcd235
Signed-off-by: Austin Schuh <austin.linux@gmail.com>
diff --git a/aos/events/logging/logfile_utils.cc b/aos/events/logging/logfile_utils.cc
index 9c7fe5d..260e368 100644
--- a/aos/events/logging/logfile_utils.cc
+++ b/aos/events/logging/logfile_utils.cc
@@ -528,7 +528,16 @@
   const monotonic_clock::time_point timestamp = result->monotonic_sent_time;
 
   newest_timestamp_ = std::max(newest_timestamp_, timestamp);
-  VLOG(2) << "Read from " << filename() << " data " << FlatbufferToJson(msg);
+
+  if (VLOG_IS_ON(3)) {
+    VLOG(3) << "Read from " << filename() << " data " << FlatbufferToJson(msg);
+  } else if (VLOG_IS_ON(2)) {
+    SizePrefixedFlatbufferVector<MessageHeader> msg_copy = msg;
+    msg_copy.mutable_message()->clear_data();
+    VLOG(2) << "Read from " << filename() << " data "
+            << FlatbufferToJson(msg_copy);
+  }
+
   return result;
 }