Re-land: Implement NativeViewAccessibilityWin using AXPlatformNodeWin.

ui/accessibility/platform/ax_platform_node.h

 // Copyright 2014 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_PLATFORM_AX_PLATFORM_NODE_H_
 #define UI_ACCESSIBILITY_PLATFORM_AX_PLATFORM_NODE_H_
 
+#include "ui/accessibility/ax_enums.h"
 #include "ui/accessibility/ax_export.h"
 #include "ui/gfx/native_widget_types.h"
 
 namespace ui {
 
 class AXPlatformNodeDelegate;
 
+// AXPlatformNode is the abstract base class for an implementation of
+// native accessibility APIs on supported platforms (e.g. Windows, Mac OS X).
+// An object that wants to be accessible can derive from AXPlatformNodeDelegate
+// and then call AXPlatformNode::Create. The delegate implementation should
+// own the AXPlatformNode instance (or otherwise manage its lifecycle).
 class AX_EXPORT AXPlatformNode {
  public:
-  // Create a platform appropriate instance.
+  // Create an appropriate platform-specific instance. The delegate owns the
+  // AXPlatformNode instance (or manages its lifecycle in some other way).
   static AXPlatformNode* Create(AXPlatformNodeDelegate* delegate);
 
+  // Cast a gfx::NativeViewAccessible to an AXPlatformNode if it is one,
+  // or return NULL if it's not an instance of this class.
+  static AXPlatformNode* FromNativeViewAccessible(
+      gfx::NativeViewAccessible accessible);
+
   // Call Destroy rather than deleting this, because the subclass may
   // use reference counting.
   virtual void Destroy() = 0;
 
+  // Get the platform-specific accessible object type for this instance.
+  // On some platforms this is just a type cast, on others it may be a
+  // wrapper object or handle.
   virtual gfx::NativeViewAccessible GetNativeViewAccessible() = 0;
 
+  // Fire a platform-specific notification that an event has occurred on
+  // this object.
+  virtual void NotifyAccessibilityEvent(ui::AXEvent event_type) = 0;
+
  protected:
   AXPlatformNode();
   virtual ~AXPlatformNode();
 };
 
 }  // namespace ui
 
 #endif  // UI_ACCESSIBILITY_PLATFORM_AX_PLATFORM_NODE_H_