Automated testing for the examples

[jeffposnick]

I'm not including this in #7, as it's going to have to be prioritized lower than that work. But I wanted to keep track of the need to create automated, end-to-end tests for each of the examples.

[jeffposnick]

I'm thinking of trying out something based on https://developers.google.com/web/updates/2017/06/headless-karma-mocha-chai

It won't have the same cross-browser capabilities that you get from using https://github.com/GoogleChrome/sw-testing-helpers, but theoretically our cross-browser testing story should already be covered by our test suite in the core Workbox project.

[jeffposnick]

Actually, nope, Karma is only for unit testing, not end-to-end tests.