[gin] add support for non-gin managed isolates in gin.

BUG=317398
R=abarth@chromium.org,aa@chromium.org

Review URL: https://codereview.chromium.org/82963002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236766 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236766