CHROMIUM: DROP: mm/oom_kill: Double-check before killing a child in our place

DROP THIS PATCH ON REBASE.

It is part of a patch series that attempts to solve similar problems
to the OOM reaper upstream.  NOTE that the OOM reaper patches weren't
backported because mm patches in general are fairly intertwined and
picking the OOM reaper without an mm expert and lots of careful
testing could cause new mysterious problems.

Compared to the OOM reaper, this patch series:
+ Is simpler to reason about.
+ Is not very intertwined to the rest of the system.
+ Can be fairly easily reasoned about to see that it should do no
  harm, even if it doesn't fix every problem.
- Can more easily get into the state where all memory reserves are
  gone, since it allows more than one task to be in "MEMDIE".
- Doesn't free memory as quickly.  The reaper kills anonymous /
  swapped memory even before the doomed task exits.
- Contains the magic "100 ms" heuristic, which is non-ideal.

Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>