Summary: Each build will have an embedded file specifying the target release channel for the build. This allows us to do some customisations, e.g. show "Insiders" label in the title and enable Sandy by default for insiders builds.
Reviewed By: jknoxville
Differential Revision: D25399045
fbshipit-source-id: 8e26d0754d0713ced823f86b30b54491d55b4d97