Switch to equalIgnoringASCIICase throughout modules/accessibility

BUG=627682

Review-Url: https://codereview.chromium.org/2793913007
Cr-Commit-Position: refs/heads/master@{#461858}
bool nodeHasRole(Node* node, const String& role) {
   if (!node || !node->isElementNode())
     return false;
 
  return equalIgnoringASCIICase(toElement(node)->getAttribute(roleAttr), role);
 }

bool nodeHasRole(Node* node, const String& role) {
   if (!node || !node->isElementNode())
     return false;
 
  return equalIgnoringCase(toElement(node)->getAttribute(roleAttr), role);
 }
