A11y: Add/refactor methods for manipulating bitfields on AXNodeData.

ui/accessibility/ax_tree_fuzzer.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/accessibility/ax_tree.h"
 
 class EmptyAXTreeDelegate : public ui::AXTreeDelegate {
  public:
   EmptyAXTreeDelegate() {}
 
@@ skipping 13 matching lines @@
                               const std::vector<Change>& changes) override {}
 };
 
 // Entry point for LibFuzzer.
 extern "C" int LLVMFuzzerTestOneInput(const unsigned char* data, size_t size) {
   ui::AXTreeUpdate initial_state;
   size_t i = 0;
   while (i < size) {
     ui::AXNodeData node;
     node.id = data[i++];
-    node.state = 0;
+    node.ClearBitfields();
     if (i < size) {
       size_t child_count = data[i++];
       for (size_t j = 0; j < child_count && i < size; j++)
         node.child_ids.push_back(data[i++]);
     }
     initial_state.nodes.push_back(node);
   }
 
   // Run with --v=1 to aid in debugging a specific crash.
   VLOG(1) << "Input accessibility tree:\n" << initial_state.ToString();
 
   EmptyAXTreeDelegate delegate;
   ui::AXTree tree;
   tree.SetDelegate(&delegate);
   tree.Unserialize(initial_state);
 
   return 0;
 }