Revert of Add fuzzer for AXTree and fix a couple of bugs it found.

ui/accessibility/ax_tree.cc

Index: ui/accessibility/ax_tree.cc
diff --git a/ui/accessibility/ax_tree.cc b/ui/accessibility/ax_tree.cc
index 0e87a7bb65d5483e8e70849610942a6413aa62b9..58f590be22dc0eb90d1601bc85631123ee5f08a4 100644
--- a/ui/accessibility/ax_tree.cc
+++ b/ui/accessibility/ax_tree.cc
@@ -243,16 +243,8 @@
   // First, delete nodes that used to be children of this node but aren't
   // anymore.
   if (!DeleteOldChildren(node, src.child_ids, update_state)) {
-    if (update_state->new_root) {
-      DestroySubtree(root_, update_state);
-
-      if (node != root_ &&
-          update_state->new_nodes.find(node) != update_state->new_nodes.end()) {
-        DestroySubtree(node, update_state);
-      }
-
-      root_ = nullptr;
-    }
+    if (update_state->new_root)
+      DestroySubtree(update_state->new_root, update_state);
     return false;
   }
 
@@ -269,7 +261,7 @@
     // DestroySubtree.
     AXNode* old_root = root_;
     root_ = node;
-    if (old_root && old_root != node)
+    if (old_root)
       DestroySubtree(old_root, update_state);
   }