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This is a regression from:
https://chromium-review.googlesource.com/c/chromium/src/+/2483342

The case under which the crash happens is when the internal cache
(URLIndexPrivateData) is being rebuilt on the history thread and
GetMostRecentVisitsForURL() returns false. I believe that basically
only happens if there is a problem with the db.

I would have liked a test for this, but there is no way to
force the db to return false.

BUG=1146970
TEST=none

Change-Id: Ied6a7e1c75ef8fcc47043d231f4877a597757bf0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2527006Reviewed-by: Justin Donnelly <jdonnelly@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825464}