Move services code brought in from Mojo to live under //third_party.

mojo/services/accessibility/public/interfaces/accessibility.mojom

-// Copyright 2014 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.
-
-module mojo;
-
-import "geometry/public/interfaces/geometry.mojom";
-
-interface AxProvider {
-  GetTree() => (array<AxNode> nodes);
-};
-
-struct AxNode {
-  // Must be non-zero.
-  uint32 id;
-
-  // Can be zero if the node has no parent or next sibling.
-  uint32 parent_id;
-  uint32 next_sibling_id;
-
-  mojo.Rect bounds;
-
-  // At most one of the below will be present.
-  // TODO(aa): These should become a union.
-  AxLink? link;
-  AxText? text;
-};
-
-struct AxLink {
-  string url;
-};
-
-struct AxText {
-  string content;
-};