Posix: fix named SHM mappings permissions.

Make sure that named mappings in /dev/shm/ aren't created with
broad permissions.

BUG=254159
R=mark@chromium.org, markus@chromium.org

Review URL: https://codereview.chromium.org/17779002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@209814 0039d316-1c4b-4281-b951-d872f2087c98
bool SharedMemory::CreateAndMapAnonymous(size_t size) {
  return CreateAnonymous(size) && Map(size);
}

bool SharedMemory::CreateAndMapAnonymous(size_t size) {
  return CreateAnonymous(size) && Map(size);
}
