Don't store the user data

Currently, some runs create a folder like
/tmp/puppeteer_dev_chrome_profile-nXlTSz
with 13Mo of data

See also:
puppeteer/puppeteer#6414

Concretely:
- Use --incognito
- Better browser close

Note the `userDataDir: '/dev/null',` will crash the tests:
Unexpected error: TargetCloseError: Protocol error (Target.createTarget): Target closed.

buildtools/check-example.js

@@ -61,13 +61,9 @@ const OSMImage = fileMock('osm.png', 'image/png');
 const ASITVDCapabilities = fileMock('asitvd.capabilities.xml', 'text/xml');
 const SgxCapabilities = fileMock('sgx.capabilities.xml', 'text/xml');
 let browser;
-let browserClosed = false;
 
 process.on('unhandledRejection', async (reason, promise) => {
   console.log('UnhandledRejection: ', promise, 'reason:', reason);
-  if (browser && !browserClosed) {
-    await browser.close();
-  }
   process.exit(2);
 });
 
@@ -88,7 +84,6 @@ function loaded(page, browser) {
         console.log(`The page take more than 60s. to load (${(new Date() - start) / 1000}).`);
         console.log('Pending requests:');
         requestsURL.forEach((request) => console.log(request));
-        await browser.close();
         process.exit(2);
       } else {
         timeout = undefined;
@@ -105,40 +100,37 @@ function loaded(page, browser) {
             .then(
               async () => {
                 console.log(`Screenshot saved at: ${screenshotPath}`);
-                await browser.close();
               },
               async (e) => {
                 console.log(`Screenshot error: ${e}`);
-                await browser.close();
                 process.exit(2);
               },
             );
         }, 1000);
-      } else {
-        await browser.close();
       }
     }
   }, 500);
 }
 (async () => {
   browser = await puppeteer.launch({
-    args: ['--no-sandbox', '--disable-web-security', '--single-process'],
+    args: ['--no-sandbox', '--disable-web-security', '--single-process', '--incognito'],
     headless: true,
   });
+  process.on('exit', (code) => {
+    browser.close();
+  });
   const page = await browser.newPage();
 
   await page.setViewport({width: 900, height: 1080});
   await page.setRequestInterception(true);
   page.on('pageerror', async (e) => {
     console.log('Page error');
     console.log(e);
-    await browser.close();
     process.exit(2);
   });
   page.on('dialog', async (e) => {
     console.log('Unexpected alert message');
     console.log(e);
-    await browser.close();
     process.exit(2);
   });
   page.on('request', (request) => {
@@ -259,7 +251,6 @@ function loaded(page, browser) {
       !url.startsWith('https://maps.googleapis.com/')
     ) {
       console.log(`Request failed on: ${url}`);
-      await browser.close();
       process.exit(2);
     }
     loaded(page, browser);
@@ -285,21 +276,16 @@ function loaded(page, browser) {
           .text()
           .includes('Multiple versions of Lit loaded. Loading multiple versions is not recommended.')
       ) {
-        await browser.close();
         process.exit(2);
       }
     }
   });
   await page.goto(page_url).catch(async (error) => {
     console.log(`Page load error: ${error}.`);
-    await browser.close();
     process.exit(2);
   });
   loaded(page, browser);
 })().catch(async (error) => {
   console.log(`Unexpected error: ${error}.`);
-  if (browser && !browserClosed) {
-    await browser.close();
-  }
   process.exit(2);
 });