Leap API for "benchmarking"

[jellyfish-linden]

It would be extremely cool if we could get a Leap API that would start recording performance metrics and one to stop it so that we could take extremely precise performance metric data in a relatively standardized way.

I'm picturing (for the API) something like:
{pump: 'Performance', data: {op: 'startRecording', filename: '/performance/metric/path'}}
For starting it and
{pump: 'Performance', data: {op: 'stopRecording'}}

and for the actual file I'm picturing something like:

{"timestamp": <time1>, "fps": <sample1>}
{"timestamp": <time2>, "fps": <sample2>}
{"timestamp": <time3>, "fps": <sample3>}
{"timestamp": <time4>, "fps": <sample4>}

Theoretically this structure could also be used to handle other metrics the viewer has internally; things like vram, memory usage, cpu usage, etc... would probably be stuff viewers would probably also want in such a tool.

Test Plan

Run these leap APIs and see if they report metrics correctly.

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[jellyfish-linden]

Actually thinking about the report file could be just a list of elapsed time since last frame similar to how fraps records benchmarks. Could even make that it's own API startFrametimesRecording and stopFrametimesRecording.

So:
Start:
{pump: 'Performance', data: {op: 'startFrametimesRecording', filename: '/performance/metric/path'}}

Stop:
{pump: 'Performance', data: {op: 'stopFrametimesRecording'}}

Log (in ms presumably):

16
16
32
16
32
16