Optimize test for pointer being in a partition on 32-bit.

We use a small (8KB) global bitmap.

R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/25640003

git-svn-id: svn://svn.chromium.org/blink/trunk@158777 bbb929c8-8fbe-4397-9dbb-9b2b20218538