Implement a reorder queue in VTVideoDecodeAccelerator.

This CL does not implement that actual computation of the order, becuase
the original plan of just copying the implementation from the VAAPI was
buggy. A second CL will follow with the computation once the bugs are
fully understood.

BUG=133828

Review URL: https://codereview.chromium.org/727893002

Cr-Commit-Position: refs/heads/master@{#305905}
2 files changed