It isn't necessary to have every file compile them, and they add unnecessary clutter in there.
Created attachment 27294 [details] Patch to fix bug (moved COMPILE_ASSERTs out of TypeTraits.h and into TypeTraits.cpp)
Comment on attachment 27294 [details] Patch to fix bug (moved COMPILE_ASSERTs out of TypeTraits.h and into TypeTraits.cpp) r=me
Applied in @r40678.