[Chromoting] Add missing file to webapp's GN build.

[Chromoting] Add missing file to webapp's GN build.

This also makes the Note at the top of the files (to keep the GYP and
GN files in sync) a bit more noticeable.

BUG=

Committed: https://crrev.com/ed09d9afa925ba6bd4fe2fa8e705ad2cc2c60e73
Cr-Commit-Position: refs/heads/master@{#327378}

[garykac, 2015-04-28 20:25:39]

garykac@chromium.org changed reviewers:
+ jamiewalch@chromium.org

[Jamie, 2015-04-28 21:10:28]

lgtm

[garykac, 2015-04-28 21:11:08]

The CQ bit was checked by garykac@chromium.org

[commit-bot: I haz the power, 2015-04-28 21:12:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1116463002/1

[commit-bot: I haz the power, 2015-04-28 22:28:22]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-28 22:29:30]

Patchset 1 (id:??) landed as
https://crrev.com/ed09d9afa925ba6bd4fe2fa8e705ad2cc2c60e73
Cr-Commit-Position: refs/heads/master@{#327378}