Cast Streaming API end-to-end browser_test.

Similar to the TabCaptureApi.EndToEnd test: An extension is run that generates a rotating cycle of colors and audio tones, and the result is captured and streamed to an in-process Cast receiver.  In addition:

1. Refactored existing code out of the cast_receiver_app into a shared InProcessReceiver class.
2. Added a convenient StandaloneCastEnvironment for test apps.
3. Got rid of the cast_receiver_app prompts since the defaults are used >99% of the time.  Using the --enable-prompts command line arg will show them again.
4. Minor clean-ups in files touched.

NOTE: The new EndToEnd test is being submitted as disabled while outstanding bugs are worked by the team.  Will re-enable once the implementation is sufficiently stable for the bots.

R=hubbe@chromium.org, kalman@chromium.org

Review URL: https://codereview.chromium.org/184813009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255805 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255805