RFR: Remove racy assert in ShenandoahResetNextMarkBitmapTraversalTask

[Roman Kennke]

> On 09/11/2018 06:04 PM, Roman Kennke wrote:
>> Right. The following makes both the order in cleanup and the
>> reset-next-markbitmap loop consistent with adaptive:
>>
>> Incremental:
>> http://cr.openjdk.java.net/~rkennke/fixtamsassert/webrev.01.diff/
>> Full:
>> http://cr.openjdk.java.net/~rkennke/fixtamsassert/webrev.01/
> 
> Looks good.
> 
> Seems to me ShenandoahResetNextBitmapTraversalTask should never experience trashed regions now.
> Which means we can simplify it like below, and this will also solidify the expectation that trashed
> regions recycling should happen before resetting the bitmaps:
>   http://cr.openjdk.java.net/~shade/shenandoah/traversal-resetbitmaps-1.patch
> 
> This passes tier3_gc_shenandoah on x86_64.
> 
> -Aleksey

Good point!

The equivalent code in ShResetNextBitmapTask checks for
is_bitmap_slice_committed(). Can this become a problem? Or is this
something to be cleaned up there?

I'll run with your patch on aarch64 and if successful, push it.

Roman