FunctionSamples::GUIDToFuncNameMap can be static instead of per
function sample. It is only used by SampleProfileLoader on a per module
basis and there's never a case (and we probably don't want such case)
that different FunctionSamples have differnet GUIDToFuncNameMap because it's
just reverse MD5 lookup!
This reduce the size of a FunctionSamples object, which has been a
bottleneck on profile loading.