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

ui/accessibility/ax_range.h

Index: ui/accessibility/ax_range.h
diff --git a/ui/accessibility/ax_range.h b/ui/accessibility/ax_range.h
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index 0000000000000000000000000000000000000000..eb08ad64c9a7e8998d224620d8809057eb42518e
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+++ b/ui/accessibility/ax_range.h
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+// 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.
+
+#ifndef UI_ACCESSIBILITY_AX_RANGE_H_
+#define UI_ACCESSIBILITY_AX_RANGE_H_
+
+#include "ui/accessibility/ax_position.h"
+
+namespace ui {
+
+// A range of ax positions.
+struct AX_EXPORT AXRange {
+  AXRange() : anchor(AXPosition()), focus(AXPosition()) {
+  }
+
+  AXRange(AXPosition anchor, AXPosition focus)
+      : anchor(anchor), focus(focus) {
+  }
+
+  virtual ~AXRange() {
+  }
+
+  bool IsNull() const { return anchor.IsNull() || focus.IsNull(); }
+
+  AXPosition anchor;
+  AXPosition focus;
+};
+
+}  // namespace ui
+
+#endif  // UI_ACCESSIBILITY_AX_RANGE_H_