GitLab

Add new gaia end point for child account signin / signup
DD: https://docs.google.com/document/d/1NJFsv7Mugy2ssYmyc3-Qh8_Ra5zwfKdeyYCFQ8WeAlQ

Bug: 1101318
Change-Id: Ia6769f01dfe9f1409ee120b9cc71ab66ae658963
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2359073
Commit-Queue: Yunke Zhou <yunkez@google.com>
Reviewed-by: Roman Sorokin [CET] <rsorokin@chromium.org>
Reviewed-by: David Roger <droger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#799570}