Drop hover:on-demand support & let touch-screens report "none" instead.

The "hover" and "any-hover" media query features was originally speced to
have three possible values {"none", "on-demand", "hover"}. The "on-demand"
value has been removed from the spec recently:
  https://drafts.csswg.org/mediaqueries-4/#hover
so we are considering removing support for this value.

Through this CL, chromium drops the support for the "on-demand" value.
Touch-screens will now report "none" instead to match mobile Safari.

Blink intent thread: https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/-sTmxMpl6iI

BUG=654861

Review-Url: https://codereview.chromium.org/2673963002
Cr-Commit-Position: refs/heads/master@{#459223}
14 files changed