tonihei 3c6ad40481 Add shuffle order interface and default implementation.
These classes maintain a shuffled order of indices allowing to query the
next, previous, first, and last indices. And also support inserting and
removing elements without changing the shuffled order of the rest.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=164116287
2017-08-03 14:49:32 +01:00
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2017-08-03 14:47:04 +01:00