[Safe Browsing] Move SafeBrowsingBlockingPageFactory to its own file

This CL moves //chrome's SafeBrowsingBlockingPageFactory and
SafeBrowsingBlockingPageFactoryImpl to their own files. This change is
in preparation for having all clients create SafeBrowsingBlockingPage
via the factory. That in turn will allow for abstraction of
//chrome-level dependencies via the factory implementation (now renamed
to ChromeSafeBrowsingBlockingPageFactory), in preparation for
componentization of SafeBrowsingBlockingPage and classes that currently
create the blocking page via
SafeBrowsingBlockingPage::CreateBlockingPage().

Bug: 1226567
Change-Id: Ie98996094b46774f276a8456a7a886f1bc18f057
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3013876


Commit-Queue: Colin Blundell <blundell@chromium.org>
Reviewed-by: Xinghui Lu <xinghuilu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#900957}