Make shared memory segments writable only by their rightful owners.

BUG=143859
TEST=Chrome's UI still works on Linux and Chrome OS
Review URL: https://chromiumcodereview.appspot.com/10854242

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@158289 0039d316-1c4b-4281-b951-d872f2087c98
void DetachSharedMemory(Display* display, XSharedMemoryId shmseg) {
  DCHECK(QuerySharedMemorySupport(display));

  XShmSegmentInfo shminfo;
  memset(&shminfo, 0, sizeof(shminfo));
  shminfo.shmseg = shmseg;

  if (!XShmDetach(display, &shminfo))
    NOTREACHED();
}

void DetachSharedMemory(Display* display, XSharedMemoryId shmseg) {
  DCHECK(QuerySharedMemorySupport(display));

  XShmSegmentInfo shminfo;
  memset(&shminfo, 0, sizeof(shminfo));
  shminfo.shmseg = shmseg;

  if (!XShmDetach(display, &shminfo))
    NOTREACHED();
}
