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(SharedMemoryHandle handle, bool read_only)
    : mapped_file_(handle),
      memory_(NULL),
      read_only_(read_only),
      created_size_(0),
      lock_(NULL) {
}

SharedMemory::SharedMemory(SharedMemoryHandle handle, bool read_only)
    : mapped_file_(handle),
      memory_(NULL),
      read_only_(read_only),
      created_size_(0),
      lock_(NULL) {
}
