misc/pprof: support web profiles on windows
misc/pprof: support web profiles on windows

LGTM=bradfitz
R=golang-codereviews, bradfitz, alex.brainman
CC=golang-codereviews
https://codereview.appspot.com/61260044

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