Port 6a628573

Original commit message:
    This reduces the reserved virtual memory size needed for the store buffer.

R=ulan@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=chromium:578883
LOG=NO

Review URL: https://codereview.chromium.org/1848983002

Cr-Commit-Position: refs/heads/master@{#35186}