RFR (M): 8184346: Clean up G1CMBitmap

[Roman Kennke]

Looks good to me.

Roman

> Hi again,
>
>   a few more cleanups could be found that were worth picking up here.
>
> On Thu, 2017-07-20 at 13:06 +0200, Thomas Schatzl wrote:
>> Hi all,
>>
>>   Erik and Mikael had a look at it and suggested several further
>> cleanups, removing about 40 LOC more. These included:
>>
>> - instead of G1CMBitMapR0 use properly const'ified G1CMBitmaps
>> - change the _start and _word_size members into an equivalent
>> MemRegion
>> - minor cleanups, removing obsolete asserts, simplify code.
>>
>> Webrevs:
>> http://cr.openjdk.java.net/~tschatzl/8184346/webrev.1_to_2/ (diff)
>> http://cr.openjdk.java.net/~tschatzl/8184346/webrev.2/ (full)
>> Testing:
>> jprt
> Webrevs:
> http://cr.openjdk.java.net/~tschatzl/8184346/webrev.2_to_3/ (diff)
> http://cr.openjdk.java.net/~tschatzl/8184346/webrev.3/ (full)
> Testing:
> jprt
>
> Thanks,
>   Thomas