Revert of This is a reland of ServiceWorkerCache::Keys.

Revert of This is a reland of ServiceWorkerCache::Keys. (patchset #3 id:70001 of https://codereview.chromium.org/528233003/)

Reason for revert:
Now getting a Valgrind leak that is likely due to this CL: 

Suppression (error hash=#935FB14CBC8B5858#):
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:_ZN9__gnu_cxx13new_allocatorIN10disk_cache20SimpleEntryOperationEE8allocateEmPKv
fun:_ZNSt11_Deque_baseIN10disk_cache20SimpleEntryOperationESaIS1_EE16_M_allocate_nodeEv
fun:_ZNSt5dequeIN10disk_cache20SimpleEntryOperationESaIS1_EE16_M_push_back_auxIJS1_EEEvDpOT_
fun:_ZNSt5dequeIN10disk_cache20SimpleEntryOperationESaIS1_EE12emplace_backIJS1_EEEvDpOT_
fun:_ZNSt5dequeIN10disk_cache20SimpleEntryOperationESaIS1_EE9push_backEOS1_
fun:_ZNSt5queueIN10disk_cache20SimpleEntryOperationESt5dequeIS1_SaIS1_EEE4pushEOS1_
fun:_ZN10disk_cache15SimpleEntryImpl5CloseEv
fun:_ZN10disk_cache12EntryDeleterclEPNS_5EntryE
fun:_ZN4base8internal15scoped_ptr_implIN10disk_cache5EntryENS2_12EntryDeleterEED2Ev
fun:_ZN10scoped_ptrIN10disk_cache5EntryENS0_12EntryDeleterEED2Ev
}

Original issue's description:
> This is a reland of ServiceWorkerCache::Keys.
> 
> Reland of https://codereview.chromium.org/477973002/
> 
> There was a memory leak.  EndEnumeration wasn't called on the iterator.  
> 
> Fixed and tested with ASAN.
> 
> The leak was detected because SimpleCache doesn't clean up its enumerators on deletion, but it should.  See https://code.google.com/p/chromium/issues/detail?id=410276
> 
> BUG=392621
> 
> Committed: https://chromium.googlesource.com/chromium/src/+/a3a3703b91203db3e2248d656b86cb26bf2e30e3

TBR=michaeln@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=392621
Committed: https://crrev.com/5b4dd4870897dfa9fe7e12e504f84d1e4dfb7302
Cr-Commit-Position: refs/heads/master@{#293373}

[jkarlin, 2014-09-04 23:22:04]

Created Revert of This is a reland of ServiceWorkerCache::Keys.

[commit-bot: I haz the power, 2014-09-04 23:24:02]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/jkarlin@chromium.org/538263002/1

[commit-bot: I haz the power, 2014-09-04 23:28:47]

Committed patchset #1 (id:1) as 2375daae28b384210b51c4991941e89537a77317

[earthdok, 2014-09-09 17:41:03]

On 2014/09/04 23:28:47, I haz the power (commit-bot) wrote:
> Committed patchset #1 (id:1) as 2375daae28b384210b51c4991941e89537a77317

I think the Valgrind leak may be a flake.

[jkarlin, 2014-09-09 17:45:11]

On 2014/09/09 17:41:03, earthdok wrote:
> On 2014/09/04 23:28:47, I haz the power (commit-bot) wrote:
> > Committed patchset #1 (id:1) as 2375daae28b384210b51c4991941e89537a77317
> 
> I think the Valgrind leak may be a flake.

I can consistently reproduce it.  Somewhere I need to let the messageloop run
before finishing a test.

[commit-bot: I haz the power, 2014-09-10 03:33:56]

Patchset 1 (id:??) landed as
https://crrev.com/5b4dd4870897dfa9fe7e12e504f84d1e4dfb7302
Cr-Commit-Position: refs/heads/master@{#293373}