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trace_events: add support for line-delimited JSON output

Rodrigo Muino Tomonari requested to merge github/fork/jasnell/trace-events-ldjson into master

Adds a new --trace-event-format command line option that may be used to specify V8 Trace Event JSON output or a line-delimited JSON variant.

By default, the V8 Trace Events format uses a root object with a single trace_events: [] property. While there are some hackish ways to process that format in a fully streaming model, newline delimited JSON is a better general approach. However, as newline delimited JSON is not yet supported by the V8 trace events viewer, it cannot be the default.

This PR adds the option of using either...

node --trace-event-format ldjson --trace-events-enabled
node --trace-event-format json --trace-events-enabled

This also gives us the option of potentially adding other formats later on down the line.

/cc @ofrobots @AndreasMadsen @mcollina @nodejs/diagnostics

Checklist
  • make -j4 test (UNIX), or vcbuild test (Windows) passes
  • tests and/or benchmarks are included
  • documentation is changed or added
  • commit message follows commit guidelines

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