Due to a bug in the version of the web-animations-next polyfill used by
Chrome MD WebUI and a new warning in Blink, page transitions trigger
a console warning:

"Specifying animation easing as a function is deprecated and all support will be removed in M54, around October 2016, at which point this will throw a TypeError. This warning may have been triggered by the Web Animations or Polymer polyfills. See  http://crbug.com/601672  for details."

We will update web-animations-js when Polymer does.