Add Clank to the gn exec_script whitelist

Add Clank to the gn exec_script whitelist

Fixes downstream gn bots affected by https://codereview.chromium.org/1063873002

TBR=brettw@chromium.org
BUG=474506
Committed: https://crrev.com/470951714e0ea3656dab463bf14dad99e83db977
Cr-Commit-Position: refs/heads/master@{#324028}

[dgn, 2015-04-07 09:52:31]

The CQ bit was checked by dgn@chromium.org

[commit-bot: I haz the power, 2015-04-07 09:52:36]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1063063002/1

[commit-bot: I haz the power, 2015-04-07 09:52:36]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-04-07 09:52:37]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer,
_not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[dgn, 2015-04-07 10:03:42]

dgn@chromium.org changed reviewers:
+ bauerb@chromium.org

[Bernhard Bauer, 2015-04-07 10:05:49]

LGTM w/ a nit:

https://codereview.chromium.org/1063063002/diff/1/.gn
File .gn (right):

https://codereview.chromium.org/1063063002/diff/1/.gn#newcode113
.gn:113: # TODO(dgn): Layer violation but breaks the build otherwise, see issue
474506.
Nit: if you write the bug as https://crbug.com/474506, it becomes clickable :)

[dgn, 2015-04-07 10:08:58]

The CQ bit was checked by dgn@chromium.org

[dgn, 2015-04-07 10:08:59]

The patchset sent to the CQ was uploaded after l-g-t-m from bauerb@chromium.org
Link to the patchset: https://codereview.chromium.org/1063063002/#ps20001
(title: "replaced issue number with a link")

[commit-bot: I haz the power, 2015-04-07 10:09:01]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1063063002/20001

[commit-bot: I haz the power, 2015-04-07 10:37:56]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-04-07 10:38:51]

Patchset 2 (id:??) landed as
https://crrev.com/470951714e0ea3656dab463bf14dad99e83db977
Cr-Commit-Position: refs/heads/master@{#324028}

[brettw, 2015-04-07 17:34:00]

LGTM. This approach is fine with me for now. If this is causing a lot of
problems we can revisit.

I hope, though, that the result is clank tries not to add exec_script calls so
it doesn't come up! :)