Ensure bad responses aren't cached

[jeffposnick]

R: @philipwalton

Fixes #2737

This was a regression introduced in Workbox v6's modified precaching logic. This PR ensures that a bad response isn't saved to the cache before installation is halted.

[philipwalton]

This approach LGTM (just noticed a few spelling/grammar issues in the comments).

One thought though: instead of adding conditionally adding and removing defaultPrecacheCacheabilityPlugin, did you consider just always adding and removing it? E.g. before the install event happens, always add it if needed and then always remove it afterward.

Since it only applies to the install event, and since you have to make the check anyway, perhaps keeping it from running during fetch events is good in general.

[jeffposnick]

After discussing offline, it's not possible for the PrecacheStrategy to run code once, at a point in time right before the install event happens. That's something that only the PrecacheController could do, and I want to ensure that PrecacheStrategy behaves properly even if it's not called by PrecacheController.