[Media Router] Assign each route a current cast mode if possible

[Media Router] Assign each route a current cast mode if possible

This change gives each media route in the WebUI a current cast mode
value if its media source corresponds to one of the currently available
cast modes. This is to prevent showing the 'cast' button that allows
replacing the route when the new route would effectively be a copy of
the original route.

BUG=614144
R=apacible@chromium.org
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:closure_compilation

[btolsch, 2016-06-06 06:27:39]

Description was changed from

==========
[Media Router] Assign each route a current cast mode if possible

This change gives each media route in the WebUI a current cast mode
value if its media source corresponds to one of the currently available
cast modes. This is to prevent showing the 'cast' button that allows
replacing the route when the new route would effectively be a copy of
the original route.

BUG=614144
R=apacible@chromium.org
==========

to

==========
[Media Router] Assign each route a current cast mode if possible

This change gives each media route in the WebUI a current cast mode
value if its media source corresponds to one of the currently available
cast modes. This is to prevent showing the 'cast' button that allows
replacing the route when the new route would effectively be a copy of
the original route.

BUG=614144
R=apacible@chromium.org
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:closure_compilation
==========