Fix conflation of !IS_ANDROID and ENABLE_EXTENSIONS.

There is a lot of code which conflates !IS_ANDROID with
ENABLE_EXTENSIONS. This makes it difficult to control building the
Extensions system.

This is one of a series of CLs to fix these issues related to the
safeBrowsingPrivate API and its implementation.

Bug: 376722712
Change-Id: Iba00dcf76fa41e146dea91b91554342fb64df0d4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5981231


Auto-Submit: David Bertoni <dbertoni@chromium.org>
Commit-Queue: Vasilii Sukhanov <vasilii@chromium.org>
Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1378920}