RFR (XS): JDK-8055635: Missing include in g1RegionToSpaceMapper.hpp results in unresolved symbol of fastdebug build without precompiled headers

[Thomas Schatzl]

Hi,

  can I have reviews for the following small change? It fixes a missing
symbol error when trying to run the VM after JDK-8038423, if the VM is
built on Linux with gcc 4.8.2-16 without precompiled headers in
fastdebug mode.

Not sure how that slipped through since I always build without
precompiled headers, but well...

CR:
https://bugs.openjdk.java.net/browse/JDK-8055635
Webrev:
http://cr.openjdk.java.net/~tschatzl/8055635/webrev/

Testing:
local testing, jprt building

Thanks,
  Thomas