[Chromoting] Update jscompile target to use JS files from gypi.

[Chromoting] Update jscompile target to use JS files from gypi.

The old version parses the main.html file to get the list of JS files
to verify. Since we're moving to auto-generate this file, we can safely get
the Js files from the same gypi since that's the same source being used
to generate the HTML file.

This also adds the WCS sandbox files to the list of JS files being checked --
they were not being checked as part of the old target because they are not
used in the main.html file.

BUG=
R=jamiewalch@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=251446

[Jamie, 2014-02-14 02:09:02]

lgtm

[garykac, 2014-02-14 19:19:48]

The CQ bit was checked by garykac@chromium.org

[commit-bot: I haz the power, 2014-02-14 19:22:45]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/garykac@chromium.org/163953011/50001

[commit-bot: I haz the power, 2014-02-14 20:49:10]

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

[commit-bot: I haz the power, 2014-02-14 20:49:10]

Retried try job too often on win_rel for step(s) browser_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win_rel&nu...

[garykac, 2014-02-15 00:20:39]

Committed patchset #3 manually as r251446 (presubmit successful).