These are very tightly coupled, and internal/protopprof is small.
There's no point to having a separate package.

Change-Id: I2c8aa49c9e18a7128657bf2b05323860151b5606
Reviewed-on: https://go-review.googlesource.com/36711
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>