Allow execution of JavaScript in Distiller pages.

Allow execution of JavaScript in Distiller pages.

We inject JavaScript into the distiller pages when we load them
for printing, so this exception is needed.

Related change https://codereview.chromium.org/1125343004/

BUG=490809

[arjunpatel, 2015-08-05 18:34:41]

arjunpatel@hp.com changed reviewers:
+ piman@chromium.org, vitalybuka@chromium.org

[Vitaly Buka (NO REVIEWS), 2015-08-05 23:12:28]

vitalybuka@chromium.org changed reviewers:
+ jochen@chromium.org

[Vitaly Buka (NO REVIEWS), 2015-08-05 23:12:28]

LGTM
+jochen, as author of https://codereview.chromium.org/1258593002

[arjunpatel, 2015-08-05 23:31:37]

The CQ bit was checked by arjunpatel@hp.com

[commit-bot: I haz the power, 2015-08-05 23:31:52]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1271313003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1271313003/1

[commit-bot: I haz the power, 2015-08-05 23:31:53]

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

[commit-bot: I haz the power, 2015-08-05 23:31:54]

The author arjunpatel@hp.com has not signed Google Contributor License
Agreement. Please visit https://cla.developers.google.com to sign and manage
CLA.

[jochen (gone - plz use gerrit), 2015-08-06 05:01:08]

not lgtm

- content must not know about the distiller, as it's a higher-level concept
- the distiller cannot guarantee that all javascript from the original website
is stripped, so it's in general not safe to interact with the main world.

please run your script in the same isolated world as the rest of the chrome
distiller does.