bindings: Ensures the object living during creating a wrapper.

V8DOMWrapper::createWrapper called in wrap() may delete the object
before the object gets associated with the wrapper which is being
created.  So we have to prevent GC to collect the object during
creating a new wrapper, especially for the case that no one except
for the new wrapper owns the object.

BUG=411735,235436

Review URL: https://codereview.chromium.org/591463002

git-svn-id: svn://svn.chromium.org/blink/trunk@182344 bbb929c8-8fbe-4397-9dbb-9b2b20218538