Fail gracefully when chromium failed to download
This patch changes both install.js and Launcher.js to inform how
chromium could be downloaded manually.
Currently, after the chromium was rolled to a new revision, the
previsious revision is kept downloaded in the puppeteer folder.
Since every revision is ~70Mb, it quickly piles up.
This patch removes previous downloaded chromium revisions after
a new one is successfully installed.
This patch:
- reformats codebase to use 2-spaces instead of 4. This will
align the project with other codebases (e.g. DevTools and Lighthouse)
- enables eslint indentation checking
References #19
This patch introduces check_availability.js utility which looks for
available chromium binaries for different revisions and platforms.
This patch also re-factors the chromium downloader scripts so that
it can operate different platforms.
