Form validation: Do not show validation bubble if the page is invisible.

BUG=673163

Review-Url: https://codereview.chromium.org/2572813003
Cr-Commit-Position: refs/heads/master@{#438476}
HTMLFormControlElement* HTMLFormControlElement::enclosingFormControlElement(
    Node* node) {
  if (!node)
    return nullptr;
  return Traversal<HTMLFormControlElement>::firstAncestorOrSelf(*node);
}

HTMLFormControlElement* HTMLFormControlElement::enclosingFormControlElement(
    Node* node) {
  if (!node)
    return nullptr;
  return Traversal<HTMLFormControlElement>::firstAncestorOrSelf(*node);
}
