WATCHLIST: Updated webcomponents category

It didn't relect recent file move.

TBR=dominicc@chromium.org,dglazkov@chromium.org
BUG=none
NOTRY=true

Review URL: https://codereview.chromium.org/227843003

git-svn-id: svn://svn.chromium.org/blink/trunk@170995 bbb929c8-8fbe-4397-9dbb-9b2b20218538