Use WriteString in hashProviderInternal

maphash.Hash implements WriteString, which avoids an allocation in
order to convert the string to a byte slice.  Using the concrete
type instead of the io.Writer interface also allows int64Array to
be allocated on the stack.

Test: SOONG_PROFILE_MEM=/tmp/mem.pprof m nothing
Change-Id: I5894f7399c2a232f5f67d7d0724a6115ba2c278f
1 file changed