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The issue was a general UBSan one, not a UBSan vptr issue. Also, we
didn't have to blacklist the false positive, but instead provided UBSan
wth the necessary type info.

BUG=737384

Change-Id: Ie6299e1edfc010ef976ab4fbefacba4d06e305b7
Reviewed-on: https://chromium-review.googlesource.com/579448Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Nicolas Capens <nicolascapens@google.com>
Cr-Commit-Position: refs/heads/master@{#488322}