PartitionAllocTest.MappingCollision still not working on Windows.

Disable it.

TBR=tsepez@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/106743004

git-svn-id: svn://svn.chromium.org/blink/trunk@163282 bbb929c8-8fbe-4397-9dbb-9b2b20218538