Creates AXPosition to uniquely identify a position in the accessibility tree

content/browser/accessibility/ax_platform_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 "content/browser/accessibility/ax_platform_position.h"
+
+#include "content/browser/accessibility/browser_accessibility_manager.h"
+
+namespace content {
+
+AXPlatformPosition::AXPlatformPosition() {}
+
+AXPlatformPosition::~AXPlatformPosition() {}
+
+int32_t AXPlatformPosition::AnchorChildID(int child_index) const {

[dmazzoni, 2016/10/18 23:59:11]

I just realized that this won't work across iframes, because the
tree ID of the child will be different.

Also PlatformGetChild() probably isn't what you want anyway, because
it excludes inline text boxes (on all platforms).

Maybe you should be using InternalGetChild / InternalChildCount, and
handle iframes separately?

+  if (child_index < 0 || child_index >= AnchorChildCount())
+    return AXPosition::INVALID_ANCHOR_ID;
+
+  BrowserAccessibility* child = GetAnchor()->PlatformGetChild(child_index);
+  DCHECK(child);
+  int32_t child_id = child->GetId();
+  DCHECK_NE(child_id, AXPosition::INVALID_ANCHOR_ID);
+  return child_id;
+}
+
+int AXPlatformPosition::AnchorChildCount() const {
+  return GetAnchor() ? static_cast<int>(GetAnchor()->PlatformChildCount()) : 0;
+}
+
+int AXPlatformPosition::AnchorIndexInParent() const {
+  return GetAnchor() ? static_cast<int>(GetAnchor()->GetIndexInParent())
+                     : AXPosition::INVALID_INDEX;
+}
+
+int32_t AXPlatformPosition::AnchorParentID() const {
+  if (!GetAnchor() || !GetAnchor()->GetParent())
+    return AXPosition::INVALID_ANCHOR_ID;
+  return GetAnchor()->GetParent()->GetId();
+}
+
+BrowserAccessibility* AXPlatformPosition::GetNodeInTree(AXTreeID tree_id,
+                                                        int32_t node_id) const {
+  if (tree_id == AXPosition::INVALID_TREE_ID ||
+      node_id == AXPosition::INVALID_ANCHOR_ID) {
+    return nullptr;
+  }
+
+  auto manager = BrowserAccessibilityManager::FromID(tree_id);
+  if (!manager)
+    return nullptr;
+  return manager->GetFromID(node_id);
+}
+
+int AXPlatformPosition::MaxTextOffset() const {
+  if (IsNullPosition())
+    return AXPosition::INVALID_OFFSET;
+
+  BrowserAccessibility* anchor = GetNodeInTree(tree_id(), anchor_id());
+  if (!anchor)
+    return AXPosition::INVALID_OFFSET;
+  return static_cast<int>(anchor->GetText().length());
+}
+
+}  // namespace content