Add simple Message struct for sorting

This is going to be the simple object used to store and sort messages
before they have been matched.  Make sure operator< works, since that's
how we'll be sorting them.

Change-Id: Icc6b8f5b62024f6cd86e11d18dde438d09a9706b
diff --git a/aos/events/logging/logfile_utils.cc b/aos/events/logging/logfile_utils.cc
index 330c78e..3a39803 100644
--- a/aos/events/logging/logfile_utils.cc
+++ b/aos/events/logging/logfile_utils.cc
@@ -461,6 +461,34 @@
   ++next_part_index_;
 }
 
+bool Message::operator<(const Message &m2) const {
+  if (this->timestamp < m2.timestamp) {
+    return true;
+  } else if (this->timestamp > m2.timestamp) {
+    return false;
+  }
+
+  if (this->channel_index < m2.channel_index) {
+    return true;
+  } else if (this->channel_index > m2.channel_index) {
+    return false;
+  }
+
+  return this->queue_index < m2.queue_index;
+}
+
+bool Message::operator>=(const Message &m2) const { return !(*this < m2); }
+
+std::ostream &operator<<(std::ostream &os, const Message &m) {
+  os << "{.channel_index=" << m.channel_index
+     << ", .queue_index=" << m.queue_index << ", .timestamp=" << m.timestamp
+     << ", .data="
+     << aos::FlatbufferToJson(m.data,
+                              {.multi_line = false, .max_vector_size = 1})
+     << "}";
+  return os;
+}
+
 SplitMessageReader::SplitMessageReader(
     const std::vector<std::string> &filenames)
     : filenames_(filenames),