a11y: Move CreateTextMarker[Range] to TextMarkerHelperMac.

ui/accessibility/ax_abstract_position.cc

+// Copyright 2017 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_abstract_position.h"
+
+namespace ui {
+
+AXPositionPointer::AXPositionPointer(AXPositionPointer&& other) = default;
+AXPositionPointer::AXPositionPointer(std::nullptr_t) {}
+AXPositionPointer::~AXPositionPointer() = default;
+
+constexpr int AXAbstractPosition::INVALID_TREE_ID;
+constexpr int32_t AXAbstractPosition::INVALID_ANCHOR_ID;
+constexpr int AXAbstractPosition::BEFORE_TEXT;
+constexpr int AXAbstractPosition::INVALID_INDEX;
+constexpr int AXAbstractPosition::INVALID_OFFSET;
+const AXPositionData AXAbstractPosition::kNullData = {
+    AXPositionKind::NULL_POSITION,
+    INVALID_TREE_ID,
+    INVALID_ANCHOR_ID,
+    INVALID_INDEX,
+    INVALID_OFFSET,
+    AX_TEXT_AFFINITY_DOWNSTREAM};
+
+}  // namespace ui