GitLab

* Remove old versions of createChildFrame.
* Add browser tests.

Related CLs:
Chromium part 1: https://codereview.chromium.org/837283003/
Blink part 1: https://codereview.chromium.org/793493003/
Blink part 2: https://codereview.chromium.org/838903002/

BUG=426512

Review URL: https://codereview.chromium.org/797813006

Cr-Commit-Position: refs/heads/master@{#313384}