Creates AXPosition to uniquely identify a position in the accessibility tree

content/browser/accessibility/ax_platform_position.cc

Index: content/browser/accessibility/ax_platform_position.cc
diff --git a/content/browser/accessibility/ax_platform_position.cc b/content/browser/accessibility/ax_platform_position.cc
new file mode 100644
index 0000000000000000000000000000000000000000..51459b69bb89775d9798a2184ed3ca0c43c883cd
--- /dev/null
+++ b/content/browser/accessibility/ax_platform_position.cc
@@ -0,0 +1,41 @@
+// 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 "content/browser/accessibility/ax_platform_position.h"
+
+#include "content/browser/accessibility/browser_accessibility_manager.h"
+
+namespace content {
+
+AXPlatformPosition::AXPlatformPosition(AXTreeID tree_id,
+                                       int32_t anchor_id,
+                                       int child_index,
+                                       int text_offset,
+                                       ui::AXPositionType type)
+    : AXPosition(tree_id, anchor_id, child_index, text_offset, type) {}
+
+AXPlatformPosition::~AXPlatformPosition() {}
+
+BrowserAccessibility* AXPlatformPosition::GetNodeInTree(AXTreeID tree_id,
+                                                        int32_t node_id) const {
+  if (IsNullPosition())
+    return nullptr;
+
+  auto manager = BrowserAccessibilityManager::FromID(tree_id);
+  if (!manager)
+    return nullptr;
+  return manager->GetFromID(node_id);
+}
+
+int AXPlatformPosition::MaxTextOffset() const {
+  if (IsNullPosition())
+    return -1;
+
+  BrowserAccessibility* anchor = GetNodeInTree(get_tree_id(), get_anchor_id());
+  if (!anchor)
+    return -1;
+  return static_cast<int>(anchor->GetText().length());
+}
+
+}  // namespace content