[BUG] browserContext.close takes too long when recording videos

[Snikanes]

Context:

• Playwright Version: 1.5.0 and 1.5.1
• Operating System: Linux
• Node.js version: 12.18.3
• Browser: Reproduced in Chromium, unsure about other browsers
• Extra: Nothing in particular

Code Snippet

import { chromium } from "playwright";

(async () => {
  const videosPath = "./videocapture"; // Make sure this directory exists
  const browser = await chromium.launch({
    headless: true, // Headless or headful makes no difference
  });
  const context = await browser.newContext({
    videosPath, // Omitting videosPath makes browserContext.close take a few milliseconds
  });
  const page = await context.newPage();

  await page.goto("https://www.google.com"); // browserContext.close takes around 1 sec if only this page is loaded
  await page.goto("https://www.vg.no"); // browserContext.close takes around 4 secs if this and preceding pages are loaded
  await page.goto("https://www.dagbladet.no"); // browserContext.close takes around 5 secs if this and preceding pages are loaded
  await page.goto("https://www.aftenposten.no"); // browserContext.close takes around 9 secs if this and preceding pages are loaded
  await page.goto("https://www.dagsavisen.no"); // browserContext.close takes around 18-31 secs if this and preceding pages are loaded

  await page.close();
  await context.close();
  await browser.close();
})();

Describe the bug
When recording videos with the new stable video recording API, I find that closing browserContexts scales badly with video length. The snippet above provides a minimal reproducible example. I haven't tested very thoroughly, but enough that I am confident that there are some performance concerns here that should be addressed.

I would expect that saving a video should add much less overhead to browserContext.close than shown above, which https://github.com/qawolf/playwright-video manages to do pretty well.