RFR: 8201647: Make initial clearing of CHeapBitMap optional

[Thomas Schatzl]

Hi,

On Tue, 2018-04-17 at 14:38 +0200, Per Liden wrote:
> CHeapBitMap objects will by default clear the underlying bitmap
> during construction. In ZGC we don't want mark bitmaps to be cleared
> on construction, since we instead do this lazily during concurrent
> marking.
> 
> This patch adds a "bool clear = true" argument to CHeapBitMap's 
> constructor to be able to opt-out of this behavior.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8201647
> Webrev: http://cr.openjdk.java.net/~pliden/8201647/webrev.0
> 
> /Per

  looks good.

Thomas