Output for an allocation and free (sweep) follows

MProf_Malloc(p=0xc2100210a0, size=0x50, type=0x0 <single object>)
        #0 0x46ee15 runtime.mallocgc /usr/local/google/home/cshapiro/go/src/pkg/runtime/malloc.goc:141
        #1 0x47004f runtime.settype_flush /usr/local/google/home/cshapiro/go/src/pkg/runtime/malloc.goc:612
        #2 0x45f92c gc /usr/local/google/home/cshapiro/go/src/pkg/runtime/mgc0.c:2071
        #3 0x45f89e mgc /usr/local/google/home/cshapiro/go/src/pkg/runtime/mgc0.c:2050
        #4 0x45258b runtime.mcall /usr/local/google/home/cshapiro/go/src/pkg/runtime/asm_amd64.s:179

MProf_Free(p=0xc2100210a0, size=0x50)
        #0 0x46ee15 runtime.mallocgc /usr/local/google/home/cshapiro/go/src/pkg/runtime/malloc.goc:141
        #1 0x47004f runtime.settype_flush /usr/local/google/home/cshapiro/go/src/pkg/runtime/malloc.goc:612
        #2 0x45f92c gc /usr/local/google/home/cshapiro/go/src/pkg/runtime/mgc0.c:2071
        #3 0x45f89e mgc /usr/local/google/home/cshapiro/go/src/pkg/runtime/mgc0.c:2050
        #4 0x45258b runtime.mcall /usr/local/google/home/cshapiro/go/src/pkg/runtime/asm_amd64.s:179

R=golang-dev, dvyukov, rsc, cshapiro
CC=golang-dev
https://golang.org/cl/21990045