pprof: problem fetching source profiles: inconsistent samples type count: 2 != 4

Please answer these questions before submitting your issue. Thanks!

### What version of pprof are you using?

```
pprof
Built on Oct 25 2018 01:08:44 (1540454924)
Built by cloud-dev-shared-releaser@oqfl3-v6.prod.google.com:/google/src/files/218645428/depot/branches/pprof_release_branch/218638946.1/OVERLAY_READONLY/google3
Built as //perftools/profiles:pprof
Built from changelist 218645428 with baseline 218645428 with version map map 0 { // } in a mint client based on //depot/branches/pprof_release_branch/218638946.1/google3
Build label: pprof_20181025_00_RC00
Build tool: Blaze, release blaze-2018.10.17-3 (mainline @217419960)
Build target blaze-out/k8-opt/bin/perftools/profiles/pprof
Built with --verifiable=true
Build FDO type: plain
Build LTO type: none
No MPM version info
```

If you are using pprof via `go tool pprof`, what's your `go env` output?
If you run pprof from GitHub, what's the Git revision?

--> Neither: it might have been pre-installed on my version of rodete.

### What operating system and processor architecture are you using?
4.17.0-3rodete2-amd64 #1 SMP Debian 4.17.17-1rodete2 (2018-08-28) x86_64 GNU/Linux
Intel(R) Xeon(R) CPU E5-1650 v3 @ 3.50GHz

### What did you do?
I was getting data that didn't look right from a C++ program, so I tried to change the sampling frequency by setting `HEAP_PROFILE_TIME_INTERVAL=10` when running my program. I also tried an interval of `2`. Now when I run:
```
pprof -http=localhost:9999 $envoy "$out_prefix"*
```

If possible, provide a recipe for reproducing the error.

--> this is possible but it involves building https://github.com/envoyproxy/envoy which has a complex build process.

Attaching a profile you are trying to analyze is good.
--> working on it

### What did you expect to see?
chrome window showing memory profile. I do get this when I don't specify the time interval. However then I get data that I don't believe. Specifically I think I'm only seeing a small number of the allocations I expect.

### What did you see instead?
```
pprof: problem fetching source profiles: inconsistent samples type count: 2 != 4
```