Add sigbjornf as platform/heap owner.

R=
BUG=
NOTRY=true

Review URL: https://codereview.chromium.org/717393004

git-svn-id: svn://svn.chromium.org/blink/trunk@185352 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/platform/heap/OWNERS

 ager@chromium.org
 erik.corry@gmail.com
 haraken@chromium.org
+sigbjornf@opera.com
 vegorov@chromium.org
 wibling@chromium.org
 zerny@chromium.org