Code:  bool AXARIAGridCell::isAriaColumnHeader() const {
   const AtomicString& role = getAttribute(HTMLNames::roleAttr);
  return equalIgnoringCase(role, "columnheader");
 }

Commit Message: Switch to equalIgnoringASCIICase throughout modules/accessibility

BUG=627682

Review-Url: https://codereview.chromium.org/2793913007
Cr-Commit-Position: refs/heads/master@{#461858}
CWE ID: CWE-254
 bool AXARIAGridCell::isAriaColumnHeader() const {
   const AtomicString& role = getAttribute(HTMLNames::roleAttr);
  return equalIgnoringASCIICase(role, "columnheader");
 }
