HashField is a 32-bit field.

R=bmeurer@chromium.org, joransiu@ca.ibm.com, michael_dawson@ca.ibm.com, mbrandy@us.ibm.com, bjaideep@ca.ibm.com
BUG=

Review-Url: https://codereview.chromium.org/2117403002
Cr-Commit-Position: refs/heads/master@{#37557}