Remove deprecated v8::External::New calls (blink side)

BUG=266838
R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/75163003

git-svn-id: svn://svn.chromium.org/blink/trunk@162193 bbb929c8-8fbe-4397-9dbb-9b2b20218538