Issue 4139 - Don't save element hiding filters on disk

This integrates changes from https://codereview.adblockplus.org/29345663/.

Repository: hg.adblockplus.org/adblockplus

[Wladimir Palant, 2016-06-17 00:11:42]

The adblockpluscore commit this relies on landed so I've updated the
dependencies file.

[Thomas Greiner, 2016-06-17 16:25:06]

Looks fine overall and I like the small improvements you made to existing code.

But what about preexisting elemhide.css files? Shouldn't we delete those when
updating to this version?

[Wladimir Palant, 2016-06-17 16:30:01]

On 2016/06/17 16:25:06, Thomas Greiner wrote:
> But what about preexisting elemhide.css files? Shouldn't we delete those when
> updating to this version?

I thought about this and the approach that Firefox usually takes is just keeping
files around. It's simpler, doesn't introduce an additional source of errors and
having these files really doesn't cost you anything. And after a few years most
profiles will be reset one way or another anyway.

[Thomas Greiner, 2016-06-17 16:43:12]

On 2016/06/17 16:30:01, Wladimir Palant wrote:
> On 2016/06/17 16:25:06, Thomas Greiner wrote:
> > But what about preexisting elemhide.css files? Shouldn't we delete those
when
> > updating to this version?
> 
> I thought about this and the approach that Firefox usually takes is just
keeping
> files around. It's simpler, doesn't introduce an additional source of errors
and
> having these files really doesn't cost you anything. And after a few years
most
> profiles will be reset one way or another anyway.

Ok, let's leave it then.

LGTM