Switch to equalIgnoringASCIICase throughout modules/accessibility

BUG=627682

Review-Url: https://codereview.chromium.org/2793913007
Cr-Commit-Position: refs/heads/master@{#461858}
bool AXObject::isButton() const {
  AccessibilityRole role = roleValue();

  return role == ButtonRole || role == PopUpButtonRole ||
         role == ToggleButtonRole;
}

bool AXObject::isButton() const {
  AccessibilityRole role = roleValue();

  return role == ButtonRole || role == PopUpButtonRole ||
         role == ToggleButtonRole;
}
