Fix integer overflow in Windows shared memory handling.

BUG=164490
Review URL: https://codereview.chromium.org/11450016

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@171369 0039d316-1c4b-4281-b951-d872f2087c98
SharedMemory::~SharedMemory() {
  Close();
  if (lock_ != NULL)
    CloseHandle(lock_);
}

SharedMemory::~SharedMemory() {
  Close();
  if (lock_ != NULL)
    CloseHandle(lock_);
}
