x/tools/cmd/heapdump: add empty heapdump command

This change creates a place where we can start building
the 'heapdump' heap viewer and analyzer

Updates golang/go#16410

Change-Id: I216e13f1ceb6790bf492cfc8cbcc4f19f12b0b9e
Reviewed-on: https://go-review.googlesource.com/25085
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
1 file changed