Looking into it. I can't repro it locally. I'll see if I can parse those proto blobs to see what the proto looks like, maybe that gives a hint.

first_status:
  os_version: ""
  firmware_version: ""
  browser_version: "61.0.3158.0"
  active_period {
    time_period {
      start_timestamp: 1499990400000
      end_timestamp: 1500076800000
    }
    active_duration: 60000
  }
  system_ram_total: 31625785344
  sound_volume: 75

device_status_:
  os_version: "0.0.0.0"
  firmware_version: ""
  browser_version: "61.0.3158.0"
  active_period {
    time_period {
      start_timestamp: 1499990400000
      end_timestamp: 1500076800000
    }
    active_duration: 60000
  }
->cpu_utilization_pct: 0
  system_ram_total: 31625785344
->system_ram_free: 25752739840
  sound_volume: 75

Looks like resource usage collection happened in between (runs on a timer every 2 minutes). The solution is to compare activity times only. CL is up: https://chromium-review.googlesource.com/c/573901/.

For the record, if you ever want to debug protos from failed tests, it's a bit tricky to deal with 0 characters in these strings. This works:

char chars[] = "\n\0\x12\0*\v61.0.3158.02\x14\n\xE\b\x80\xB8\x94\xF3\xD3+\x10\x80\xF0\xAD\x9C\xD4+\x10\xE0\xD4\x3p\x80\xE0\xAC\xE8u\x98\x1K";
first_status.ParseFromArray(chars, arraysize(chars) - 1);

Note the -1 to remove 0 terminator.

To print out the proto in a human-readable format, it has to be compiled as full proto, not light:

- In third_party/protobuf/BUILD.gn, move all sources from protobuf_full to protobuf_lite_sources
- Remove option optimize_for = LITE_RUNTIME; from proto files you want to print
- LOG(INFO) << first_status.DebugString();

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9d23034c583ce7219b4d2c9a5ef9bb6b8205a63e

commit 9d23034c583ce7219b4d2c9a5ef9bb6b8205a63e
Author: Lutz Justen <ljusten@chromium.org>
Date: Mon Jul 17 09:37:29 2017

Fix flakyness in DeviceStatusCollectorTest

DeviceStatusCollector collects resource usage stats every 2 minutes.
The ActivityTimesKeptUntilSubmittedSuccessfully test compared two
full instances of DeviceStatusReportRequest. In one run of the test,
the test failed because the resource usage collection happened right
in between. This CL compares activity times only (aka what the test
is interested in) and removes the full status comparison.

Also fixes an uninteresting mock function call and moves some
functions from public to protected.

BUG= chromium:743061 
TEST=out/Release/browser_tests --gtest_filter=DeviceStatusCollectorTest.*

Change-Id: I39d65260794326cae90d57ec583ff28e2d9a9092
Reviewed-on: https://chromium-review.googlesource.com/573901
Reviewed-by: Drew Wilson <atwilson@chromium.org>
Commit-Queue: Lutz Justen <ljusten@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487034}
[modify] https://crrev.com/9d23034c583ce7219b4d2c9a5ef9bb6b8205a63e/chrome/browser/chromeos/policy/device_status_collector_browsertest.cc

Thanks for the proto debugging steps! I was completely lost there.

Also thanks for the fix!