Add a random name to anonymous shared memory sections

      This prevents Windows from ignoring the DACL on unnamed sections.

BUG=338538
R=cpu@chromium.org,brettw@chromium.org

Review URL: https://codereview.chromium.org/412043002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@285195 0039d316-1c4b-4281-b951-d872f2087c98