Revert of ReReland ServiceWorkerCacheStorage::Keys function (patchset #3 id:140001...

Revert of ReReland ServiceWorkerCacheStorage::Keys function (patchset #3 id:140001 of https://codereview.chromium.org/543093003/)

Reason for revert:
Linux Valgrind now passes but ChromeOS Valgrind doesn't.  Looks like I need to do more on TearDown.

Original issue's description:
> ReReland ServiceWorkerCacheStorage::Keys function
>
> Suppression (error hash=#E226F7559AD360E7#):
> For more info on using suppressions see http://dev.chromium.org/developers/tree-sheriffs/sheriff-details-chromium/memory-sheriff#TOC-Suppressing-memory-reports
> {
> <insert_a_suppression_name_here>
> Memcheck:Leak
> fun:_Znw*
> fun:_ZN4base8internal20PostTaskAndReplyImpl16PostTaskAndReplyERKN15tracked_objects8LocationERKNS_8CallbackIFvvEEESA_
> fun:_ZN4base10TaskRunner16PostTaskAndReplyERKN15tracked_objects8LocationERKNS_8CallbackIFvvEEES9_
> fun:_ZN10disk_cache15SimpleEntryImpl13CloseInternalEv
> fun:_ZN10disk_cache15SimpleEntryImpl24RunNextOperationIfNeededEv
> fun:_ZN10disk_cache15SimpleEntryImpl21DoomOperationCompleteERKN4base8CallbackIFviEEENS0_5StateEi
> }
> Original CL: https://codereview.chromium.org/477973002/
> Reland: https://codereview.chromium.org/528233003/
>
> The SimpleCache backend wasn't given a chance to finish up a close operation before the IO messageloop closed at the end of functions.  The tests now run the loop in TearDown.
>
> The original patch is PatchSet1 and the fix is PatchSet3.
>
> BUG=392621
>
> Committed: https://crrev.com/bbfe6ce49b8e99b190085dffbf446b474c5f07ff
> Cr-Commit-Position: refs/heads/master@{#294090}

TBR=michaeln@chromium.org,horo@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=392621

Review URL: https://codereview.chromium.org/562613002

Cr-Commit-Position: refs/heads/master@{#294150}