[Files.app] Initial implementation of new audio player

Implements the new audio player of Files.app. See the issue for detail. Although it has still room to implement and improve, but basically it works.

BUG=273308
TEST=manually tested
R=dgozman@chromium.org, mtomasz@chromium.org

Review URL: https://codereview.chromium.org/144883002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247833 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247833