Render sharing flows inside the container

This renders the Data Sharing SDK inside the container, and sets up theming using GM3 variable names.

Change-Id: I432b7c47be701be15b6e6366ee0ca4d415e8c577
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5877031
Reviewed-by: pengchao Cai <pengchaocai@chromium.org>
Commit-Queue: Travis Crumley <crumley@google.com>
Reviewed-by: Yuheng Huang <yuhengh@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1362050}