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* Replace various implementation of these helpers throughout //fuchsia
  with a common helper.
* Replace a stale bug reference.

Bug: 978696
Change-Id: I7bf29ea00312bfcaa3baff8f8d3f5a724367fc12
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1733419
Commit-Queue: Fabrice de Gans-Riberi <fdegans@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#684166}