Make ScriptPromiseProperty GarbageCollectedFinalized.

Off-heap ScriptPromiseProperty with an on-heap holder has a leak.
Hence this CL makes ScriptPromiseProperty an on-heap class.

This CL also fixes the problem that on-heap ScriptPromiseProperty
can't work with un-traceable types, such as integers, V8UndefinedType,
and so on.

BUG=363967
R=dominicc, haraken

Review URL: https://codereview.chromium.org/399203003

git-svn-id: svn://svn.chromium.org/blink/trunk@178748 bbb929c8-8fbe-4397-9dbb-9b2b20218538