Since Node 10, `console.assert` no longer throws an AssertionError.
(This is generally good since it aligns Node.js with Browsers.)
This patch migrates all usages of `console.assert` in our codebase.
- All the `lib/` and testing code is migrated onto a handmade `assert`
function. This is to make Puppeteer transpilation / bundling easier.
- All the tooling is switched to use Node's `assert` module.
Fixes#2547.
This patch introduces `BrowserFetcher` class that manages
downloaded versions of products.
This patch:
- shapes Downloader API to be minimal yet usable for our needs. This
includes removing such methods as `Downloader.supportedPlatforms` and
`Downloader.defaultRevision`.
- makes most of the fs-related methods in Downloader async. The only
exception is the `Downloader.revisionInfo`: it has stay sync due to the
`pptr.executablePath()` method being sync.
- updates `install.js` and `utils/check_availability.js` to use new API
- finally, renames `Downloader` into `BrowserFetcher`
Fixes#1748.
