IsWitnessEnabled() should not be called from libconsensus code, only from outside what's already encapsulated.
The 3 callers already AssertLockHeld(cs_main);, this is my grep:
./src/main.h:448:bool ContextualCheckBlock(const CBlock& block, CValidationState& state, CBlockIndex *pindexPrev);
./src/main.cpp:3525:bool ContextualCheckBlock(const CBlock& block, CValidationState& state, CBlockIndex * const pindexPrev)
./src/main.cpp:3602: return state.DoS(100, error("ContextualCheckBlock(): cost limit failed"), REJECT_INVALID, "bad-blk-cost");
./src/main.cpp:3689: if ((!CheckBlock(block, state, chainparams.GetConsensus(), GetAdjustedTime())) || !ContextualCheckBlock(block, state, pindex->pprev)) {
./src/main.cpp:3780: if (!ContextualCheckBlock(block, state, pindexPrev))
I could have said this during segwit review instead of now, sorry @sipa.
