[Chromoting] Extract shared viewport code into viewport.js.

[Chromoting] Extract shared viewport code into viewport.js.

Currently the shared code is located in desktop_viewport.js, which means
that this file needs to be included by the AppRemoting builds. But
including that file also brings in a bunch of DesktopRemoting stuff as
well.

This cl extracts out the shared code into viewport.js (and moves the
unittests as well) so that we can more easily exclude the desktop
code from the AppRemoting code in a following cl.

BUG=

Committed: https://crrev.com/828a33d42acb4e738cba6d6b2cd342a37dcdfc83
Cr-Commit-Position: refs/heads/master@{#327053}

[garykac, 2015-04-24 22:13:34]

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

[kelvinp, 2015-04-24 22:16:34]

lgtm

[garykac, 2015-04-27 15:32:34]

The CQ bit was checked by garykac@chromium.org

[commit-bot: I haz the power, 2015-04-27 15:32:40]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1109453005/1

[commit-bot: I haz the power, 2015-04-27 16:23:56]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-27 16:24:47]

Patchset 1 (id:??) landed as
https://crrev.com/828a33d42acb4e738cba6d6b2cd342a37dcdfc83
Cr-Commit-Position: refs/heads/master@{#327053}