Revert of offset namespace ids

Revert of offset namespace ids (patchset #7 id:120001 of https://codereview.chromium.org/881253004/)

Reason for revert:
Tests now only work if they ran in the "right" order. DOMStorageContextImplTest.Basic fails if the tests are shuffled:

content_unittests --gtest_filter=DOMStorageContextImplTest.*:DOMStorageAreaTest.* --gtest_shuffle

Original issue's description:
> [DOMStorage] Offset the session storage namespace ids generated by different contexts to help identify when an id from one is mistakenly used in another.
>
> Committed: https://crrev.com/36dcef3da5317365ab95e50a5f6b7fa98ada1d5e
> Cr-Commit-Position: refs/heads/master@{#314256}

TBR=jsbell@chromium.org,michaeln@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Committed: https://crrev.com/7bdc4a49e605261b60ee1339f93e835d853bf645
Cr-Commit-Position: refs/heads/master@{#314274}

[Lei Zhang, 2015-02-03 05:40:14]

Created Revert of offset namespace ids

[commit-bot: I haz the power, 2015-02-03 05:40:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/896733002/1

[commit-bot: I haz the power, 2015-02-03 05:41:48]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-03 05:42:38]

Patchset 1 (id:??) landed as
https://crrev.com/7bdc4a49e605261b60ee1339f93e835d853bf645
Cr-Commit-Position: refs/heads/master@{#314274}