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Upon presubmit, will perform the following checks if histograms.xml,
obsolete_histograms.xml or enums.xml is changed.

- Validate prefix and pretty-print if histograms.xml is changed.
- Pretty-print if enums.xml is changed.
- Validate histograms contained are all obsolete if obsolete_histograms.xml
is changed.

Amended relevant files to take in relative path to a distributed histograms
directory as system argument.

Bug: 692201
Change-Id: I1797c0b65b53462cbb73820d8416a28651d1c65e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2359714
Commit-Queue: Weilun Shi <sweilun@chromium.org>
Auto-Submit: Weilun Shi <sweilun@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Cr-Commit-Position: refs/heads/master@{#800378}