Simplify MixedContentChecker::HandleCertificateError

1. Settings are the same for all the frames on the page,
so we don't need to call EffectiveFrameForFrameType.
2. Check for top-level frame outside.

This change allows to call HandleCertificateError for main
resources outside of FrameFetchContext.

Bug: 855189
Change-Id: If7aba4a8039ddcfecd4e831f4eefde41f65c4a8b
Reviewed-on: https://chromium-review.googlesource.com/c/1450424
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#628955}
4 files changed