Add live region root to the cached properties of an AXObject.

Source/core/accessibility/AXScrollView.cpp

Index: Source/core/accessibility/AXScrollView.cpp
diff --git a/Source/core/accessibility/AXScrollView.cpp b/Source/core/accessibility/AXScrollView.cpp
index 70a7c94cdceb56e03eb295fe453bf47c6fe67938..4a7ccc6f1ad37ff7523eba127dc18fa3b0c9e0c4 100644
--- a/Source/core/accessibility/AXScrollView.cpp
+++ b/Source/core/accessibility/AXScrollView.cpp
@@ -143,11 +143,21 @@ void AXScrollView::clearChildren()
 
 bool AXScrollView::computeAccessibilityIsIgnored() const
 {
+    // We just want to match whatever's returned by our web area, which is a child of this
+    // object. Normally cached attribute values may only search up the tree. We can't just
+    // call accessibilityIsIgnored on the web area, because the web area may search up its
+    // ancestors and call this function recursively, and we'd loop until a stack overflow.
+
+    // Instead, we first update the cached accessibilityIsIgnored value for this node to
+    // false, call accessibilityIsIgnored on the web area, then return the mathcing value.
+    m_cachedIsIgnored = false;
+    m_lastModificationCount = axObjectCache()->modificationCount();
+
     AXObject* webArea = webAreaObject();
-    if (!webArea)
-        return true;
+    if (webArea)
+        return webArea->accessibilityIsIgnored();
 
-    return webArea->accessibilityIsIgnored();
+    return true;
 }
 
 void AXScrollView::addChildren()