Include an empty file - this will be filled with Polymer 2 specific code
later, and it's useful to have the empty file now because the Polymer 2
change will likely be pending very long, and we would like to avoid
conflicts keeping so many files in a pending change for long.
Also include a harmless polyfill that we need for Polymer 2.
Change-Id: I504e52ae937edff1d35b29700882b522ef4dbc64
62909358e7