This patch:
* unifies assets between tests
* enables a few puppeteer tests on Puppeteer-Firefox
Drive-by: beautify failing output of `expect.toEqual` matcher.
References #3889
This patch aligns Puppeteer testing infrastructure with the approach
we use in Puppeteer-Firefox.
This patch:
- makes all tests accept Puppeteer object as a function argument
rather than require it statically. This way we can pass either
Puppeteer or Puppeteer-Firefox to drive tests.
- renames the `puppeteer.spec.js` into `launcher.spec.js`. The
`puppeteer.spec.js` is now the entry point for all cross-browsers
tests.
