Avoid updateStyleAndLayoutTree in determineAccessibilityRole

This patch avoids updating layout tree in
AXNodeObject::determineAccessibilityRole().

Element::isFocusable() requires styles to be updated. However, when
layout code calls determineAccessibilityRole(), updating layout tree
should be avoided since it may destroy the calling object.

This patch replaces it to supportsFocus(), since the main purpose is
to give elements with tabIndex explicitly set get some role.

This is a speculative fix.

BUG=590369, 647602, 665168

Review-Url: https://codereview.chromium.org/2532023002
Cr-Commit-Position: refs/heads/master@{#435009}

third_party/WebKit/Source/modules/accessibility/AXNodeObject.cpp

@@ -527,11 +527,11 @@ AccessibilityRole AXNodeObject::determineAccessibilityRole() {
     return role;
   if (getNode()->isElementNode()) {
     Element* element = toElement(getNode());
-    if (element->isInCanvasSubtree()) {
-      getDocument()->updateStyleAndLayoutTreeForNode(element);
-      if (element->isFocusable())
-        return GroupRole;
-    }
+    // A generic element with tabIndex explicitly set gets GroupRole.
+    // The layout checks for focusability aren't critical here; a false
+    // positive would be harmless.
+    if (element->isInCanvasSubtree() && element->supportsFocus())
+      return GroupRole;
   }
   return UnknownRole;
 }