Call HeapObjectHeader::checkHeader solely for its side-effect.

This requires changing its signature. This is a preliminary stage to making it
private.

BUG=633030

Review-Url: https://codereview.chromium.org/2698673003
Cr-Commit-Position: refs/heads/master@{#460489}
bool LargeObjectPage::contains(Address object) {
  return roundToBlinkPageStart(getAddress()) <= object &&
         object < roundToBlinkPageEnd(getAddress() + size());
}

bool LargeObjectPage::contains(Address object) {
  return roundToBlinkPageStart(getAddress()) <= object &&
         object < roundToBlinkPageEnd(getAddress() + size());
}
