Revert of views: Move TOOLKIT_VIEWS definition in //ui/views/ from root.

Revert of views: Move TOOLKIT_VIEWS definition in //ui/views/ from root. (patchset #6 id:100001 of https://codereview.chromium.org/1175603002/)

Reason for revert:
Speculative revert to fix win unit_test failures. https://build.chromium.org/p/chromium.win/builders/Win7%20Tests%20%281%29/builds/39651

Original issue's description:
> views: Move TOOLKIT_VIEWS definition in //ui/views/ from root.
>
> If 'toolkit_views' gyp/gn flag is toggled, then it shouldn't cause targets that
> do not depend on views to be rebuilt. To make this happen, remove the definition
> of the TOOLKIT_VIEWS flag from the top-level config into a config in views, so
> that only targets that explicitly depend on views get the define, and are
> affected by the switch.
>
> BUG=500004
> R=ben@chromium.org, sky@chromium.org
>
> Committed: https://chromium.googlesource.com/chromium/src/+/c13fc9ff0aedca62ebfdfc27d44c6b5ac204c9d8

TBR=ben@chromium.org,sky@chromium.org,sadrul@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=500004
Committed: https://crrev.com/ecbf7e40116d555c11ee958b6339618920d11c2c
Cr-Commit-Position: refs/heads/master@{#334820}

[phoglund_chromium, 2015-06-17 13:41:56]

Created Revert of views: Move TOOLKIT_VIEWS definition in //ui/views/ from root.

[commit-bot: I haz the power, 2015-06-17 13:42:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1192583002/1

[commit-bot: I haz the power, 2015-06-17 13:44:15]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-17 13:45:03]

Patchset 1 (id:??) landed as
https://crrev.com/ecbf7e40116d555c11ee958b6339618920d11c2c
Cr-Commit-Position: refs/heads/master@{#334820}

[phoglund_chromium, 2015-06-17 19:20:34]

On 2015/06/17 13:45:03, commit-bot: I haz the power wrote:
> Patchset 1 (id:??) landed as
> https://crrev.com/ecbf7e40116d555c11ee958b6339618920d11c2c
> Cr-Commit-Position: refs/heads/master@{#334820}

It appears this revert did not help. Feel free to unrevert when the current
sheriff says so (the tree is a bit of mess right now so I don't dare unrevert
right now). Sorry about the trouble.

[paulmeyer, 2015-06-17 21:19:31]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/1182053007/ by paulmeyer@chromium.org.

The reason for reverting is: Unreverting because this CL did not end up being
the problem..