It is time.

ui/accessibility/ax_tree_update.h

-// Copyright 2013 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.
-
-#ifndef UI_ACCESSIBILITY_AX_TREE_UPDATE_H_
-#define UI_ACCESSIBILITY_AX_TREE_UPDATE_H_
-
-#include <vector>
-
-#include "ui/accessibility/ax_node_data.h"
-
-namespace ui {
-
-// An AXTreeUpdate is a serialized representation of an atomic change
-// to an AXTree. The sender and receiver must be in sync; the update
-// is only meant to bring the tree from a specific previous state into
-// its next state. Trying to apply it to the wrong tree should immediately
-// die with a fatal assertion.
-//
-// An AXTreeUpdate consists of an optional node id to clear (meaning
-// that all of that node's children and their descendants are deleted),
-// followed by an ordered vector of AXNodeData structures to be applied
-// to the tree in order.
-//
-// Suppose that the next AXNodeData to be applied is |node|. The following
-// invariants must hold:
-// 1. Either |node.id| is already in the tree, or else the tree is empty,
-//        |node| is the new root of the tree, and
-//        |node.role| == WebAXRoleRootWebArea.
-// 2. Every child id in |node.child_ids| must either be already a child
-//        of this node, or a new id not previously in the tree. It is not
-//        allowed to "reparent" a child to this node without first removing
-//        that child from its previous parent.
-// 3. When a new id appears in |node.child_ids|, the tree should create a
-//        new uninitialized placeholder node for it immediately. That
-//        placeholder must be updated within the same AXTreeUpdate, otherwise
-//        it's a fatal error. This guarantees the tree is always complete
-//        before or after an AXTreeUpdate.
-struct AX_EXPORT AXTreeUpdate {
-  AXTreeUpdate();
-  ~AXTreeUpdate();
-
-  // The id of a node to clear, before applying any updates,
-  // or 0 if no nodes should be cleared. Clearing a node means deleting
-  // all of its children and their descendants, but leaving that node in
-  // the tree. It's an error to clear a node but not subsequently update it
-  // as part of the tree update.
-  int node_id_to_clear;
-
-  // A vector of nodes to update, according to the rules above.
-  std::vector<AXNodeData> nodes;
-
-  // Return a multi-line indented string representation, for logging.
-  std::string ToString() const;
-
-  // TODO(dmazzoni): location changes
-};
-
-}  // namespace ui
-
-#endif  // UI_ACCESSIBILITY_AX_TREE_UPDATE_H_