Simplify typeof_test chain_sense calculation
Simplify typeof_test chain_sense calculation

Summary:
This logic was added in D18496275, which also added the relevant testing. This
is a mechanical transformation of the code, so behavior is 100% preserved, but I
find this quite a bit easier to understand.

Reviewed By: panagosg7

Differential Revision: D20627358

fbshipit-source-id: 693f580ce53521f8b0dca8d4a9a6a2968933b329

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