bindings: Adds createPersistentHandle to WrapperTypeInfo.

Adds createPersistentHandle so that we can create a new Persistent<T> without knowing type T.  This change will be used in http://crrev.com/478243002 .

BUG=235436

Review URL: https://codereview.chromium.org/495033003

git-svn-id: svn://svn.chromium.org/blink/trunk@180886 bbb929c8-8fbe-4397-9dbb-9b2b20218538