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*Allow optionally enforcing that the name ends with a zero-length label
 (the root label).
*Add additional validation that the name doesn't use DNS name
 compression, and that the name is within the max DNS name length.
*Add an overload that takes a BigEndianReader as input. Better supports
 parsing within a DNS message when the name needs to be parsed to know
 its total length and where the next data starts after the name.

These improvements should be useful in parsing HTTPS records.

Bug: 1138620
Change-Id: Ice66aa880a8c5407af3bfd9a14d720d518ae2136
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2493153
Commit-Queue: Eric Orth <ericorth@chromium.org>
Reviewed-by: Dan McArdle <dmcardle@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821794}