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When ReturnsValidPath() fails it just returned false, with no indication
as to which of the several checks was the issue. This adds printing of
specifics, including the path when applicable. This will help with
future failures and with an ongoing investigation.

Bug: 1053446
Change-Id: I8071df44b20af482a0387e2f8558d878de6d05b1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2065358Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#743366}