GitLab

Passing unique_ptr to AddChildView as recommended.
Moved some default values to the header file too.

Change-Id: I72f4ca718bf2ac55615a51072b97b970d254e8c6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2134175Reviewed-by: Keith Lee <keithlee@chromium.org>
Commit-Queue: Darren Shen <shend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#756561}