Base class of all media renderers. Provides the common renderer functionality
of medias.
The current common functionality shared by Medias is to have an outer frame
that gets highlighted on mouse hover.
TODO(user): implement more common UI behavior, as needed.
NOTE(user): I am not enjoying how the subclasses are changing their state
through setState() ... maybe provide abstract methods like
goog.ui.media.MediaRenderer.prototype.preview = goog.abstractMethod;
goog.ui.media.MediaRenderer.prototype.play = goog.abstractMethod;
goog.ui.media.MediaRenderer.prototype.minimize = goog.abstractMethod;
goog.ui.media.MediaRenderer.prototype.maximize = goog.abstractMethod;
and call them on this parent class setState ?