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* Dramatically simplifies the test code, plus tests the public API rather than
  an internal API method.
* Declares said internal API method with private visibility.
* Updates a non-const reference returned type to be a pointer instead.
* Tucks an enum into the anonymous namespace in the implementation file.
* Fixes up some comments: clearer phrasing, plus fixed typos and wrapping.

R=holte@chromium.org

Bug: 727984
Change-Id: I4c394d04cb4f4d24cdcc8a7baa2db54f4dc5c8f7
Reviewed-on: https://chromium-review.googlesource.com/826493Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524276}