BrowserAccessibility should own a AXPlatformNode.

content/browser/accessibility/browser_accessibility.h

 // Copyright (c) 2012 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 CONTENT_BROWSER_ACCESSIBILITY_BROWSER_ACCESSIBILITY_H_
 #define CONTENT_BROWSER_ACCESSIBILITY_BROWSER_ACCESSIBILITY_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 375 matching lines @@
 
   // The manager of this tree of accessibility objects.
   BrowserAccessibilityManager* manager_;
 
   // The underlying node.
   ui::AXNode* node_;
 
   // A unique ID, since node IDs are frame-local.
   int32_t unique_id_;
 
+  // The ui platform backend

[dmazzoni, 2017/03/21 16:45:00]

nit: Make comments full sentences, end with a period.

I'd make this comment a bit more detailed so it's more clear what we're
doing here during the transition period. Something like:

// The platform-specific object that implements the accessibility APIs for this
node.
// Currently some of the platform-specific code is implemented by subclasses of
// BrowserAccessibility and some by |platform_node_|, but eventually we want all
// of that code to be in AXPlatformNode.  http://crbug.com/xxxxxx

+  ui::AXPlatformNode* platform_node_;
+
  private:
   // |GetInnerText| recursively includes all the text from descendants such as
   // text found in any embedded object. In contrast, |GetText| might include a
   // special character in the place of every embedded object instead of its
   // text, depending on the platform.
   base::string16 GetInnerText() const;
 
   // If a bounding rectangle is empty, compute it based on the union of its
   // children, since most accessibility APIs don't like elements with no
   // bounds, but "virtual" elements in the accessibility tree that don't
   // correspond to a layed-out element sometimes don't have bounds.
   void FixEmptyBounds(gfx::RectF* bounds) const;
 
   DISALLOW_COPY_AND_ASSIGN(BrowserAccessibility);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_ACCESSIBILITY_BROWSER_ACCESSIBILITY_H_