Enable TabManager to kill foreground Android apps.

Enable TabManager to kill foreground Android apps.

In the past TabManager never kill Android apps which are visible to
users (whether it's in the foreground or not). It basically only kills
Android background processes with no GUI. On machines with limited
memory it may be necessary to kill visible Android apps as well so the
system can run smoothly.

BUG=b:36207466
TEST=samus

[cylee1, 2017-03-15 14:03:58]

The CQ bit was checked by cylee@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-03-15 14:04:16]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[bccheng1, 2017-03-15 14:20:39]

bccheng@google.com changed reviewers:
+ bccheng@google.com

[bccheng1, 2017-03-15 14:20:40]

Should we avoid focused_apps but just kill visible_apps?

[semenzato, 2017-03-16 17:26:33]

On 2017/03/15 14:20:40, bccheng1 wrote:
> Should we avoid focused_apps but just kill visible_apps?

What if we only have visible apps left?  Shouldn't we also kill those in LRU
order?

The alternatives are:

1. let the kernel OOM killer kill them
2. panic

[semenzato, 2017-03-16 17:28:30]

On 2017/03/16 17:26:33, semenzato wrote:
> On 2017/03/15 14:20:40, bccheng1 wrote:
> > Should we avoid focused_apps but just kill visible_apps?
> 
> What if we only have visible apps left?  Shouldn't we also kill those in LRU
> order?
> 
> The alternatives are:
> 
> 1. let the kernel OOM killer kill them
> 2. panic

I meant "what if we have only focused apps left".
Actually, in theory there is only ONE focused app, right?
It may still be better to kill it than let the browser crash or the system
panic.

[teravest, 2017-04-12 19:33:46]

On 2017/03/16 17:28:30, semenzato wrote:
> On 2017/03/16 17:26:33, semenzato wrote:
> > On 2017/03/15 14:20:40, bccheng1 wrote:
> > > Should we avoid focused_apps but just kill visible_apps?
> > 
> > What if we only have visible apps left?  Shouldn't we also kill those in LRU
> > order?
> > 
> > The alternatives are:
> > 
> > 1. let the kernel OOM killer kill them
> > 2. panic
> 
> I meant "what if we have only focused apps left".
> Actually, in theory there is only ONE focused app, right?
> It may still be better to kill it than let the browser crash or the system
> panic.

Is this change still being considered? Just curious if this is something we'll
try.