service worker: Improve consistency around provider type functions.

For ServiceWorkerProviderHost:
* Remove IsHostToRunningServiceWorker(). This was a subtle function
since it was used mainly as !IsProviderForClient(), but it was
also false when the service worker was still starting up.
* Add IsProviderForServiceWorker() as an analogue to
IsProviderForClient().
* Improve documentation/terminology throughout for consistency
with ServiceWorkerProviderContext.

Change-Id: I69a0449aeda41f23f41bee767524aebf5ff9b1d2
TBR: kinuko
Reviewed-on: https://chromium-review.googlesource.com/1002216
Commit-Queue: Matt Falkenhagen <falken@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Makoto Shimazu <shimazu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549439}
5 files changed