added SizeMap::MaybeSizeClass
added SizeMap::MaybeSizeClass

Because it allows us to first check for smaller sizes, which is most
likely.

chencl/gperftools,romange/gperftools,acmorrow/gperftools,romange/gperftools,acmorrow/gperftools,alk/gperftools,romange/gperftools,chencl/gperftools,gshirishfree/gperftools,gperftools/gperftools,gshirishfree/gperftools,romange/gperftools,rzinsly/gperftools,rzinsly/gperftools,alk/gperftools,acmorrow/gperftools,gshirishfree/gperftools,alk/gperftools,gshirishfree/gperftools,xiaoyur347/gperftools,gperftools/gperftools,gperftools/gperftools,acmorrow/gperftools,xiaoyur347/gperftools,alk/gperftools,rzinsly/gperftools,xiaoyur347/gperftools,rzinsly/gperftools,chencl/gperftools,gperftools/gperftools,chencl/gperftools,xiaoyur347/gperftools