[Chromoting] Add GN build support for ar_sample_app target.

[Chromoting] Add GN build support for ar_sample_app target.

This adds GN build rules for the AppRemoting sample app.
Some DesktopRemoting build rules were prettified as part of this
process (to make the App- and Desktop- remoting build rules more
similar).

This re-re-lands crrev.com/1126393002 without any additional changes
required. The original issues with the GN clobber builds are fixed in
crrev.com/1137753002. The 2nd attempt to land was rejected due to
a merge race (fixed in this cl).

BUG=471916
Committed: https://crrev.com/c1fd3a3d2e9c4f8117ab6650289cebc0bb9553e7
Cr-Commit-Position: refs/heads/master@{#330243}

[garykac, 2015-05-15 22:33:50]

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

[garykac, 2015-05-15 22:33:51]

Third time's a charm!  Changes from last version noted.

https://codereview.chromium.org/1143643003/diff/1/remoting/remoting_version.gni
File remoting/remoting_version.gni (right):

https://codereview.chromium.org/1143643003/diff/1/remoting/remoting_version.g...
remoting/remoting_version.gni:18: remoting_version_files = [
This is now public (by removing the leading '_') so that it can be used as a dep
in other targets.

https://codereview.chromium.org/1143643003/diff/1/remoting/webapp/files.gni
File remoting/webapp/files.gni (right):

https://codereview.chromium.org/1143643003/diff/1/remoting/webapp/files.gni#n...
remoting/webapp/files.gni:243: "crd/js/video_frame_recorder.js",
These changes update GN to match the current GYP version.

[Jamie, 2015-05-15 22:39:48]

lgtm

[garykac, 2015-05-15 22:54:19]

The CQ bit was checked by garykac@chromium.org

[commit-bot: I haz the power, 2015-05-15 22:55:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1143643003/1

[commit-bot: I haz the power, 2015-05-16 00:21:13]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-18 11:29:40]

Patchset 1 (id:??) landed as
https://crrev.com/c1fd3a3d2e9c4f8117ab6650289cebc0bb9553e7
Cr-Commit-Position: refs/heads/master@{#330243}