RFR: non-PCH build broken again

[Aleksey Shipilev]

On 04/10/2018 10:08 PM, Zhengyu Gu wrote:
> Non-PCH build broken again.
> 
> Webrev: http://cr.openjdk.java.net/~zgu/shenandoah/sh-jdk-non-PCH-again/webrev.00/

Don't you want to include iterator.hpp instead of forward-declaring BoolObjectClosure?

Otherwise good!

-Aleksey