Added support for header and footer inside other sections, according to HTML API Mappings 1.0.

ui/accessibility/ax_position.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_node.h"
+
+namespace ui {
+
+AXPosition::AXPosition() : anchor_(nullptr), offset(-1) {}
+
+AXPosition::AXPosition(AXNode* anchor, int offset)
+    : anchor_(anchor), offset_(offset) {
+  DCHECK(anchor);
+  DCHECK_GE(offset, 0);
+}
+
+AXPosition::~AXPosition() {
+}
+
+bool AXPosition::IsNull() const {
+  return anchor_ == nullptr;
+}
+
+AXPosition AXPosition::ToLeafEquivalent() const {
+  if (IsNull())
+    return AXPosition();
+
+  if (!anchor_->child_count())
+    return AXPosition(anchor_, offset_);
+
+  if (offset_ >= anchor_->child_count())
+    return AXPosition();
+
+  AXNode* child = anchor_->children()[offset_];
+  DCHECK(child);
+  while (child->children()[0])
+    child = child->children()[0];
+  return AXPosition(child, 0);
+}
+
+AXPosition AXPosition::GetCorrespondingPositionInParent(
+    const AXNode& parent) const {
+  auto parent_node = const_cast<AXNode*>(&parent);
+  AXNode* current_node = anchor_;
+  while (current_node && parent_node != current_node->parent())
+    current_node = current_node->parent();
+
+  if (!current_node)
+    return AXPosition();
+
+  return AXPosition(parent_node, current_node->index_in_parent());
+}
+
+}  // namespace ui