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Currently committed safebrowsing interstitials are not supported
in weblayer. This patch adds this support and tests.

In this patch:
 - add support for committed interstitials for safebrowsing in
   weblayer (i.e. when kCommittedSBInterstitials is enabled).
 - add SafeBrowsingBlockingPage and SafeBrowsingNavigationThrottle
 - make SafeBrowsingBrowserTest work when kCommittedSBInterstitials
   feature is enabled.
 - parameterize tests to run both with committed interstitials and
   non-committed interstitials.

BUG=1042662
TBR=vakh@chromium.org

Change-Id: I5f732c1f0c2c6c09b2041ea0a7c8d41e81bce9d7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2003857
Commit-Queue: Tim Volodine <timvolodine@chromium.org>
Reviewed-by: Richard Coles <torne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#734515}