Revert of https://codereview.chromium.org/98443004/
Reason for revert: WTF_PartitionAlloc.MappingCollision failing on windows

TBR=tsepez@chromium.org,cevans@chromium.org
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/94013003

git-svn-id: svn://svn.chromium.org/blink/trunk@163175 bbb929c8-8fbe-4397-9dbb-9b2b20218538