Factor out JsonOptions into a struct

Change-Id: I2441069e86ea2eb95d8e1952be7c2a7a43036c74
diff --git a/aos/events/logging/log_edit.cc b/aos/events/logging/log_edit.cc
index ff263f8..0dca904 100644
--- a/aos/events/logging/log_edit.cc
+++ b/aos/events/logging/log_edit.cc
@@ -18,8 +18,7 @@
     "If provided, this is the path to the JSON with the log file header.");
 
 int main(int argc, char **argv) {
-  gflags::SetUsageMessage(
-      R"(This tool lets us manipulate log files.)");
+  gflags::SetUsageMessage(R"(This tool lets us manipulate log files.)");
   aos::InitGoogle(&argc, &argv);
 
   if (!FLAGS_header.empty()) {
@@ -53,7 +52,8 @@
     } else {
       aos::logger::MessageReader reader(FLAGS_logfile);
       aos::util::WriteStringToFileOrDie(
-          FLAGS_header, aos::FlatbufferToJson(reader.log_file_header(), true));
+          FLAGS_header, aos::FlatbufferToJson(reader.log_file_header(),
+                                              {.multi_line = true}));
     }
   }