Revert of Disable failing blink_style.key_mobile_sites (patchset #1 id:1 of https://codereview.chromium.org/2758533003/ )

Reason for revert:
Root cause should be fixed.

Original issue's description:
> Disable failing blink_style.key_mobile_sites
>
> BUG=702194
>
> Review-Url: https://codereview.chromium.org/2758533003
> Cr-Commit-Position: refs/heads/master@{#457432}
> Committed: https://chromium.googlesource.com/chromium/src/+/4d954851ba9c129b4529302f77862f6b812165d8

TBR=sullivan@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=702194

Review-Url: https://codereview.chromium.org/2768683005
Cr-Commit-Position: refs/heads/master@{#458730}
1 file changed