Revert of Add Keys() function to ServiceWorkerCache.

Revert of Add Keys() function to ServiceWorkerCache. (patchset #13 id:280001 of https://codereview.chromium.org/477973002/)

Reason for revert:
Failing on content_unittests

EmptyKeys_1
TwoKeys_1
TwoKeysThenOne_1

on Linux ASAN LSAN

Original issue's description:
> Add Keys() function to ServiceWorkerCache.
> 
> Other changes:
> * Introduced a ReadHeaders helper function which reads headers from a cache entry into a protobuf.  This is used by Match() and Keys().
> 
> 
> BUG=392621
> 
> Committed: https://chromium.googlesource.com/chromium/src/+/02812f0a3edcacca1f7e05ea0a47cb3d8c6025e1

TBR=michaeln@chromium.org,gavinp@chromium.org,jkarlin@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=392621
Committed: https://crrev.com/01bc0b71ce5b347c646cc08309ab7bc08fb966cb
Cr-Commit-Position: refs/heads/master@{#292970}

[scottmg, 2014-09-02 18:18:14]

Created Revert of Add Keys() function to ServiceWorkerCache.

[commit-bot: I haz the power, 2014-09-02 18:20:15]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/scottmg@chromium.org/534683002/1

[commit-bot: I haz the power, 2014-09-02 18:59:41]

Committed patchset #1 (id:1) as 597fcff6df18a7e61a8d8d94ead1233b001b6c4e

[commit-bot: I haz the power, 2014-09-10 03:19:49]

Patchset 1 (id:??) landed as
https://crrev.com/01bc0b71ce5b347c646cc08309ab7bc08fb966cb
Cr-Commit-Position: refs/heads/master@{#292970}