Rather than maintain our own test runner we should instead lean on the community and use Mocha which is very popular and also our test runner of choice in DevTools too.
Note that this commit doesn't remove the TestRunner source as it's still used for other unit tests, but they will be updated in a future PR and then we can remove the TestRunner.
The main bulk of this PR is updating the tests as the old TestRunner passed in contextual data via the `it` function callback whereas Mocha does not, so we introduce some helpers for the tests to make it easier.
This patch:
- introduces new testRunner methods `addTestDSL` and `addSuiteDSL`
to add annotated test / suite.
- introduces new test/suite declaration methods: `it_fails_ffox` and
`describe_fails_ffox`. These are equal to `it`/`describe` for chromium
tests and to `xit`/`xdescribe` for firefox.
- marks all unsupported tests with `it_fails_ffox`
- adds a new command-line flag `'--firefox-status'` to `//test/test.js`.
This flag dumps current amount of tests that are intentionally skipped
for Firefox.
End goal: get rid of all `it_fails_ffox` and `describe_fails_ffox`
tests.
Drive-By: remove cookie tests "afterEach" hook that was removing
cookies - it's not needed any more since every test is run in a
designated browser context.
References #3889
