Node perf tester

[TimvdLippe]

Add a node interface for the perf-tester. It uses chrome headless if no port is specified. It parses a series of options which it will navigate to, perform the timings and then extract window.perfTiming from the Runtime.

[sorvell]

These should be removed, right?

[sorvell]

The diff here is weird. What happened?

[TimvdLippe]

The line endings were mixed. I changed all lines to LF.

[TimvdLippe]

@sorvell I updated the line endings, so the diff is less nice 😢 I updated console._perfEnd to take an options object to disable the force layout, as well as expose the actual timing in window.perfTiming, such that the node script can use it. I also added some documentation on how to use the script.

[hastebrot]

I updated the line endings, so the diff is less nice

Using w=1 (ignore whitespace; similar to git diff --ignore-all-space) in the URL for the diff viewer (compare) helps a bit:
https://github.com/PolymerLabs/perf-tester/pull/4/files?diff=unified&w=1