G1Mux2Closure is used by verification to verify and in case of error print out g1 specific error messages.

However, since G1Mux2Closure is an OopClosure, it is actually wrapped by NoHeaderExtendedOopClosure in oop_iterate* calls. ExtendedOopClosure has its own verification that is very generic, and may trigger in the same situations as G1Mux2Closure.

Disable this implicit verification for G1Mux2Closure so that we always get the g1 specific error messages.