GitLab

Migrates the crostini_browser_proxy component under the crostini_page
to Polymer3.

Change-Id: Ic4f7ca3ccbacea64e84cf02a29460dabef774efc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2640757Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Commit-Queue: Juliet Levesque <julietlevesque@google.com>
Cr-Commit-Position: refs/heads/master@{#846375}