Added a UseCounter for hover:on-demand media query parsing.

BUG=654861,689527
TBR=rkaplow@chromium.org

Review-Url: https://codereview.chromium.org/2678933002
Cr-Commit-Position: refs/heads/master@{#448407}
(cherry picked from commit 324495d3549f08062867c366e4ed2f23d83d78bb)

Review-Url: https://codereview.chromium.org/2682073004 .
Cr-Commit-Position: refs/branch-heads/2987@{#388}
Cr-Branched-From: ad51088c0e8776e8dcd963dbe752c4035ba6dab6-refs/heads/master@{#444943}
3 files changed