Make skobes a core/rendering/OWNER

Skobes has 60 patches in core/rendering[1] including work deep in layout
for text autosizing, and scrollbar code.

[1] git shortlog --author=skobes Source/core/rendering/ | wc -l

R=dsinclair,pdr

Review URL: https://codereview.chromium.org/725273002

git-svn-id: svn://svn.chromium.org/blink/trunk@185394 bbb929c8-8fbe-4397-9dbb-9b2b20218538