Revert of [Android Refactor] Merge WebappDataStorage#LAST_USED_UNSET and LAST_USED_INVALID (patchset #1 id:1 of https://codereview.chromium.org/2927723003/ )
Reason for revert:
Spec revert due to significantly increased flakiness in one of the WebApkUpdateManagerTests: https://bugs.chromium.org/p/chromium/issues/detail?id=731485
Original issue's description:
> [Android Refactor] Merge WebappDataStorage#LAST_USED_UNSET and LAST_USED_INVALID
>
> Having both LAST_USED_UNSET and LAST_USED_INVALID is unnecessary as
> - the "last_used" SharedPreference should never be set to LAST_USED_INVALID
> - there isn't any logic which checks whether "last_used" is LAST_USED_INVALID
>
> Additionally, this CL renames LAST_USED_INVALID to TIMESTAMP_INVALID as
> the getters for several time-based SharedPreferences other than "last_used"
> return LAST_USED_INVALID if the preference is unset.
>
> BUG=None
>
> Review-Url: https://codereview.chromium.org/2927723003
> Cr-Commit-Position: refs/heads/master@{#478067}
> Committed: https://chromium.googlesource.com/chromium/src/+/618fd4f3564ecc43f4f7bff660c22a9dd5fc2309
TBR=dominickn@chromium.org,pkotwicz@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=None
Review-Url: https://codereview.chromium.org/2928993004
Cr-Commit-Position: refs/heads/master@{#478154}
5 files changed
