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This CL implements routines for serializing and deserializing object
ids, which simplifies the logic for storing topics which were already
registered for.

TBR: pavely@chromium.org
Bug: 867402, 801985
Change-Id: Ie859cc87b8e9b3cff54ae2af0eeed68467af09af
Reviewed-on: https://chromium-review.googlesource.com/1154921Reviewed-by: Pavel Yatsuk <pavely@chromium.org>
Reviewed-by: Cait Phillips <caitkp@chromium.org>
Reviewed-by: Jan Krcal <jkrcal@chromium.org>
Commit-Queue: Tatiana Gornak <melandory@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583991}