runtime/debug: skip TestWriteHeapDumpNonempty on NaCl. TestWriteHeap is useless on NaCl anyway.
runtime/debug: skip TestWriteHeapDumpNonempty on NaCl.
TestWriteHeap is useless on NaCl anyway.

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://codereview.appspot.com/101980048

tv42/old-go,pombredanne/go-deleteme,pombredanne/go-deleteme,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,tv42/old-go,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,tv42/old-go,pombredanne/go-deleteme,tv42/old-go,tv42/old-go