Remote DevTools expensive layout

go.js

const fs = require('fs')
const CDP = require('chrome-remote-interface')

let traceStr = ''
let allEvts = [];

function delay(ms) {
	return new Promise(resolve => setTimeout(resolve, ms))
}

function printLayouts(data) {
	const evts = data.value || data
	evts.forEach(evt => {
		allEvts.push(evt)
		if (!/layout/.test(evt.name)) return
		if (!evt.dur) console.log(evt)
		console.log('layout evt!', evt.dur)
	})
}

CDP.New().then(target => CDP({target})).then(client => {
	const {Page, Tracing, IO, Network, Runtime, Emulation} = client

function handleTraceAsEvts() {
	
			Tracing.dataCollected(printLayouts);
			Tracing.tracingComplete(() => {
				fs.writeFileSync('trace.json', JSON.stringify({traceEvents: allEvts}))
				setTimeout(() =>client.close(), 50)
			})
			Tracing.end()
}


function handleTraceAsStream() {
	Tracing.tracingComplete(data => { 

		function handleTraceRead(resp) {
			traceStr += resp.data
			if (resp.eof) {
				printLayouts(JSON.parse(traceStr).traceEvents)
				fs.writeFileSync('trace.json', traceStr)
				setTimeout(() => client.close(), 50)
				return
			}

			IO.read({handle: data.stream}).then(handleTraceRead)
		}

		IO.read({handle: data.stream}).then(handleTraceRead)
	})
	Tracing.end()

}

	const categories = [
      '-*', // exclude default
      'toplevel',
      'blink.console',
      'blink.user_timing',
      'benchmark',
      'loading',
      'latencyInfo',
      'devtools.timeline',
      'disabled-by-default-devtools.timeline',
      'disabled-by-default-devtools.timeline.frame',
      'disabled-by-default-devtools.timeline.stack',
      // Flipped off until bugs.chromium.org/p/v8/issues/detail?id=5820 is fixed in Stable
      // 'disabled-by-default-v8.cpu_profiler',
      // 'disabled-by-default-v8.cpu_profiler.hires',
      'disabled-by-default-devtools.screenshot'
    ].join(',')

	return Promise.all([
		Page.enable(),
		// Network.enable(),
		// Runtime.enable(),
		// Tracing.enable(),
	])
	// .then(() => Emulation.setCPUThrottlingRate({rate: 6}))
	// .then(() => Network.emulateNetworkConditions({latency: 562, downloadThroughput: 209715, offline: false, uploadThroughput: 20000}))
	// .then(Page.navigate({url: 'about:blank'}))
	// .then(() => delay(300))
	.then(() => {		
		Page.loadEventFired(msg => {
			console.log(msg)
			setTimeout(() => {
				handleTraceAsEvts()
				// handleTraceAsStream()


			}, 500)
		})
	})
	.then(() => Tracing.start({categories, 
      // transferMode: 'ReturnAsStream',
      // options: 'sampling-frequency=10000'  // 1000 is default and too slow.
	  }))

	.then(() => Page.navigate({url: 'http://localhost:8000/build/es6-bundled/'}))
}).catch(err => {
	console.error(err);
	process.exit(1);
})