Revert of Make the EarlyInitStartup Code Default

Revert of Make the EarlyInitStartup Code Default (patchset #1 id:1 of https://codereview.chromium.org/1453923002/ )

Reason for revert:
Backing out to see the effect on the perf graphs.

Original issue's description:
> Make the EarlyInitStartup Code Default
>
> We're satisfied with the performance characteristics of running Extension
> Feature Initialization on a background thread that we'd like to do it
> all the time now.
>
> BUG=470743
>
> Committed: https://crrev.com/697fb4718088e9b87a30f21f57168af70ef273ae
> Cr-Commit-Position: refs/heads/master@{#360352}

TBR=jochen@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=470743
Committed: https://crrev.com/5a3b884c06e2d9f263bb4b5ac8f1c94906ca57cc
Cr-Commit-Position: refs/heads/master@{#360822}

[robliao, 2015-11-20 15:12:31]

Created Revert of Make the EarlyInitStartup Code Default

[commit-bot: I haz the power, 2015-11-20 15:12:45]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1467503002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1467503002/1

[commit-bot: I haz the power, 2015-11-20 15:13:32]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-20 15:14:40]

Patchset 1 (id:??) landed as
https://crrev.com/5a3b884c06e2d9f263bb4b5ac8f1c94906ca57cc
Cr-Commit-Position: refs/heads/master@{#360822}