This factors out the element insertion code, so that it can be reused
elsewhere in a follow-up CL.

Change-Id: Ic085c8359b3024f381803ce64b49e976018277f9
Reviewed-on: https://chromium-review.googlesource.com/1010068Reviewed-by: Mythri Alle <mythria@chromium.org>
Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52592}