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In this patch:
- add skeleton classes such as UrlCheckerDelegateImpl, UI manager,
- add safebrowsing for weblayer feature,
- add safebrowsing throttle,
- add build configs, deps and owners files.

In the skeleton classes most methods are not implemented yet and
will be implemented where necessary in further CLs. Also proper
init sequence will be implemented separately.

BUG=1015418

Change-Id: I80a9a40b18204e760289c7f01a48c69370f6d7c5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1866832
Commit-Queue: Tim Volodine <timvolodine@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708672}