Add DocumentExecCommandInJavaScript.js to Blink platform resources.

Add DocumentExecCommandInJavaScript.js to Blink platform resources.

This prepares for landing of
http://crrev.com/530663002

which now requires a three-sided change due to changes in how Blink accesses
private script resources.

Part 1: http://crrev.com/583753003

BUG=408887
TEST=n/a; no code changes

Committed: https://crrev.com/8bf3d4139bce38e8eb711c6d7a66744699859008
Cr-Commit-Position: refs/heads/master@{#297130}

[yosin_UTC9, 2014-09-19 08:03:46]

Patchset #1 (id:1) has been deleted

[yosin_UTC9, 2014-09-24 04:00:01]

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

[yosin_UTC9, 2014-09-24 04:00:01]

Could you review this patch, similar to http://crrev.com/556793006, which added
PluginPlaceholderElement.js?

Thanks in advance.

[yosin_UTC9, 2014-09-26 01:21:42]

ping...

[jochen (gone - plz use gerrit), 2014-09-26 19:45:54]

lgtm

[yosin_UTC9, 2014-09-29 01:05:16]

The CQ bit was checked by yosin@chromium.org

[commit-bot: I haz the power, 2014-09-29 01:05:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/588473003/20001

[commit-bot: I haz the power, 2014-09-29 02:12:18]

Committed patchset #1 (id:20001) as de4e340dda44cfaff1e2e422a2be458a5e372762

[commit-bot: I haz the power, 2014-09-29 02:12:54]

Patchset 1 (id:??) landed as
https://crrev.com/8bf3d4139bce38e8eb711c6d7a66744699859008
Cr-Commit-Position: refs/heads/master@{#297130}