The only change in visible behaviour from that CL is that we can now report FAILED from Lock() operations.  I'll see if I can provoke that by closing the handle before trying to re-Lock() a region, or something. :)

I'm unable to coax the OS API into failing, so I can't really construct a test for this :-/

nyquist: Any suggestions?

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/97dd531b30a7089ee1d69da22ab4bacaf4883ac3

commit 97dd531b30a7089ee1d69da22ab4bacaf4883ac3
Author: Wez <wez@chromium.org>
Date: Thu Aug 31 01:26:51 2017

Add test that Lock() returns failed if ashmem_pin_region() fails.

To cause ashmem_pin_region() to fail, we arrange for it to be called with
an invalid file-descriptor, which requires a valid-looking fd (i.e. we
can't just Close() |memory|), but one on which the operation is invalid.

We can overwrite the |memory| fd with a handle to a different file using
dup2(), which has the nice properties that |memory| still has a valid fd
that it can close, etc without errors, but on which ashmem_pin_region()
will fail.

dup2() will close the ashmem file description before duplicating our
dummy file into the |memory| fd.

Bug:  752441 
Change-Id: I4c6ecced69a2817ec7d86da0e783b9f6e1d238f0
Reviewed-on: https://chromium-review.googlesource.com/602395
Commit-Queue: Wez <wez@chromium.org>
Reviewed-by: Tommy Nyquist <nyquist@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#498706}
[modify] https://crrev.com/97dd531b30a7089ee1d69da22ab4bacaf4883ac3/base/memory/discardable_shared_memory_unittest.cc