Cleanup: Remove unneeded extensions #includes.

Cleanup: Remove unneeded extensions #includes.

Also put some extensions #includes behind ENABLE_EXTENSIONS.

Committed: https://crrev.com/ceb89f23e5b89463295bdca9d8b2babaa4e26a1e
Cr-Commit-Position: refs/heads/master@{#300168}

[Lei Zhang, 2014-10-17 18:57:41]

thestig@chromium.org changed reviewers:
+ rdsmith@chromium.org

[Lei Zhang, 2014-10-17 18:57:42]

There's a couple downloads file here. Hope you don't mind reviewing the whole
thing. It's just shuffling #includes around.

[Randy Smith (Not in Mondays), 2014-10-17 19:43:34]

So, just to be clear, I'm not an expert on extensions.  Having said that, I
don't see much of a way that this could compile and be wrong.  LGTM (whole
thing).

[Lei Zhang, 2014-10-17 21:26:47]

The CQ bit was checked by thestig@chromium.org

[commit-bot: I haz the power, 2014-10-17 21:27:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/657643003/1

[commit-bot: I haz the power, 2014-10-17 22:00:03]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-10-17 22:01:31]

Patchset 1 (id:??) landed as
https://crrev.com/ceb89f23e5b89463295bdca9d8b2babaa4e26a1e
Cr-Commit-Position: refs/heads/master@{#300168}