RenderFrameImpl: unify error page handling

This patch makes CommitFailedNavigation not use
LoadNavigationErrorPage, which is left for loading
renderer-initiated error pages. That allows us
to simplify LoadNavigationErrorPage and unify all three
renderer-initiated calls.

Bug: 855189
Change-Id: Ic56fe7b63376e0c4d92d4fb38b87e9d20aae85a5
Reviewed-on: https://chromium-review.googlesource.com/c/1338919
Reviewed-by: Charlie Reis <creis@chromium.org>
Reviewed-by: Arthur Sonzogni <arthursonzogni@chromium.org>
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612270}
2 files changed