Simplify insertion of text track container

We want the element to be the first child of the overlay enclosure, which
can be expressed in a slightly more straight-forward manner without and
if-else.

BUG=447161

Review URL: https://codereview.chromium.org/847493002

git-svn-id: svn://svn.chromium.org/blink/trunk@188156 bbb929c8-8fbe-4397-9dbb-9b2b20218538
1 file changed
tree: d3cac00addb18d643ecbc3773fd51532eb5f4f0a
  1. third_party/