Proto profile conversion is inconsistent about call vs return PCs in
profile locations. The proto defines locations to be call PCs. This is
what we do when proto-izing CPU profiles, but we fail to convert the
return PCs in memory and count profile stacks to call PCs when
converting them to proto locations.

Fix this in the heap and count profile conversion functions.
TestConvertMemProfile also hard-codes this failure to convert from
return PCs to call PCs, so fix up the addresses in the synthesized
profile to be return PCs while checking that we get call PCs out of
the conversion.

Change-Id: If1fc028b86fceac6d71a2d9fa6c41ff442c89296
Reviewed-on: https://go-review.googlesource.com/42951
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>