Add --tracing to benchmarks

.gitignore

@@ -8,3 +8,6 @@ lib
 sandbox/node_modules
 *.log
 test-results.json
+mount-deep-tree-trace.json
+mount-wide-tree-trace.json
+update-dynamic-styles-trace.json

.npmignore

@@ -9,5 +9,8 @@ lib
 sandbox/node_modules
 *.log
 test-results.json
+mount-deep-tree-trace.json
+mount-wide-tree-trace.json
+update-dynamic-styles-trace.json
 
 benchmarks

benchmarks/run-headless.js

@@ -2,26 +2,34 @@ const path = require('path');
 const puppeteer = require('puppeteer');
 
 const tests = ['Mount deep tree', 'Mount wide tree', 'Update dynamic styles'];
+const tracing = process.argv.some(arg => arg.indexOf('tracing') > -1);
+
+if (tracing) {
+  console.log('\nTracing enabled. (note that this might impact benchmark results, we recommend leaving this turned off unless you need a trace)')
+}
 
 (async () => {
   console.log('\nStarting headless browser...')
   const browser = await puppeteer.launch();
   const page = await browser.newPage();
-  await page.tracing.start({ path: 'benchmark-trace.json' });
   console.log('Opening benchmark app...')
   await page.goto(`file://${path.join(__dirname, './dist/index.html')}`);
 
-  console.log('Running benchmarks... (this may take a minute; do not use your machine while these are running!)')
+  console.log('Running benchmarks... (this may take a minute or two; do not use your machine while these are running!)')
   for (var i = 0; i < tests.length; i++) {
     const test = tests[i];
+    const traceFile = `${test.toLowerCase().replace(/\s/g, '-')}-trace.json`;
     // styled-components is auto-selected, so all we gotta do is select the benchmark and press "Run"
     await page.select('[data-testid="benchmark-picker"]', test);
     await page.waitForSelector('[data-testid="run-button"]')
+    if (tracing) await page.tracing.start({ path: traceFile });
     await page.click('[data-testid="run-button"]')
     await page.waitForSelector(`[data-testid="${test} results"]`)
+    if (tracing) await page.tracing.stop();
     const result = await page.$eval(`[data-testid="${test} results"]`, node => node.innerText)
     console.log(`\n---${test}---`)
     console.log(result)
+    console.log('Trace written to', traceFile)
   }
 
   console.log('Done!')