storage: Make QuotaClient refcounted

Currently, QuotaClient is a raw pointer, jointly owned by QuotaManager
and AppCacheServiceImpl, with a complicated keep_alive dance and
conditional self-destruction.

This is just a drive-by cleanup to get rid of "raw new" calls that
looked suspicious and to make the refcounting explicit.

Once AppCache gets removed, it seems possible to make QuotaClient
to be owned fully by QuotaManager as a unique_ptr.

Change-Id: I4df4bda44f51666e99880812c49ff76a7635c13d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1949579
Auto-Submit: enne <enne@chromium.org>
Commit-Queue: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#721906}
44 files changed