[autotest] Adds chromecast deps, server, client test for sonic.

Adds an autotest dependency that installs the freshest
version of the chromecast extension as an autotest dep.

Also adds a server and client test for sonic that installs the
extension and performs a tab cast, and starts the youtube/netflix apps.
The tests will only work when the DUT and the sonic device are on
the same subnet.

TEST=emerge-lumpy autotest-deps, ran a test that uses it.
     Ran the tests, visually verified results.
BUG=chromium:321177, chromium:321179, chromium:292640

Change-Id: I48a6149a11d3bb8167a1c766873e672b3523d769
Reviewed-on: https://chromium-review.googlesource.com/179407
Commit-Queue: Prashanth B <beeps@chromium.org>
Tested-by: Prashanth B <beeps@chromium.org>
Reviewed-by: Dan Shi <dshi@chromium.org>
18 files changed