Add size() to expose amount of requests in queue

[StephanBijzitter]

R: @jeffposnick @tropicadri

Fixes #2940

In short, this allows a developer to perform a quick count of what's left in the queue, so that a number could be displayed in a status indicator... or whatever else the developer wants to do with the number.

It's not as heavy as (await queue.getAll()).length and doesn't modify the queue

• ensure that gulp build && gulp lint test passes locally.

Well, I tried... but Windows doesn't very much like the npm scripts and as such I had to bypass the git hooks as well, it just wouldn't run.. Hopefully I managed to keep everything consistent with the surrounding code :-)

[jeffposnick]

Thanks for submitting this!

We have a lot of workbox-background-sync feature requests open at the moment, and I have to admit that it's one of the areas of the Workbox codebase that I am personally less familiar with. I'm going to take some time to look at this change and see whether it also address some of the other open issues.

(Regarding running the gulp tasks, apologies about that. I'll take a look at our new setup and figure out the Windows compatibility story.)

[jeffposnick]

I'd like @tropicadri to get a chance to review this, as she's touched the IndexedDB code most recently, but generally speaking, this looks like it would be useful as implemented.

[tropicadri]

LGTM Thank you!

[tropicadri]

I'd like @tropicadri to get a chance to review this, as she's touched the IndexedDB code most recently, but generally speaking, this looks like it would be useful as implemented.

I checked it out, I agree with you :)