Add OriginSafeMethodSetterCallback

OriginSafeMethodSetter is missing a callback.
This adds one.

TBR=haraken

Review URL: https://codereview.chromium.org/77793002

git-svn-id: svn://svn.chromium.org/blink/trunk@162354 bbb929c8-8fbe-4397-9dbb-9b2b20218538