GitLab

Change the bookmarks Web UI to use a browser proxy for communication
with C++. Also update tests to use a test version of the proxy
instead of registering test message handlers in C++.

Bug: 1022213
Change-Id: I7a824d51e1fdaa02e57baa44c555c634f8e230b1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1906959
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#714368}