Revert of Disable two tests in mojo_system_unittests that are suspected to be timing out (patchset #2 id:20001 of https://codereview.chromium.org/2497203002/ )

Reason for revert:
Issue 663998 still persists after this CL.

Original issue's description:
> Disable two tests in mojo_system_unittests that are suspected to be timing out
>
> BUG=663998
> TBR=pdr@chromium.org, timloh@chromium.org
>
> Committed: https://crrev.com/aae520affa1d2c4397bf4d4758a9ff48d5a0cc88
> Cr-Commit-Position: refs/heads/master@{#431847}

TBR=
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=663998

Review-Url: https://codereview.chromium.org/2504533002
Cr-Commit-Position: refs/heads/master@{#432117}


CrOS-Libchrome-Original-Commit: ba86cdb48c680aa78a142dee329d1c57ba22b00a
2 files changed
tree: 7f090049663ff58202fe4408f6a481be23cf79e6
  1. base/
  2. build/
  3. components/
  4. dbus/
  5. device/
  6. ipc/
  7. mojo/
  8. testing/
  9. third_party/
  10. ui/