Migrate BrowserAccessibility windows unique id handling to AXPlatformNodeWin.

ui/accessibility/platform/ax_platform_node.h

Index: ui/accessibility/platform/ax_platform_node.h
diff --git a/ui/accessibility/platform/ax_platform_node.h b/ui/accessibility/platform/ax_platform_node.h
index 7204c23aa884b031f962973aa268a9e2b7656420..526efe440dcdc310b4c021f88c6700ab7ae7be29 100644
--- a/ui/accessibility/platform/ax_platform_node.h
+++ b/ui/accessibility/platform/ax_platform_node.h
@@ -30,6 +30,9 @@ class AX_EXPORT AXPlatformNode {
   static AXPlatformNode* FromNativeViewAccessible(
       gfx::NativeViewAccessible accessible);
 
+  // Return the node with the given unique id.
+  static AXPlatformNode* GetFromUniqueId(int32_t unique_id);
+
   // Call Destroy rather than deleting this, because the subclass may
   // use reference counting.
   virtual void Destroy();
@@ -50,8 +53,9 @@ class AX_EXPORT AXPlatformNode {
   AXPlatformNode();
   virtual ~AXPlatformNode();
 
-  virtual AXPlatformNode* GetFromUniqueId(int32_t unique_id);
+  virtual int32_t unique_id() const;
 
+ private:
   int32_t unique_id_;
 };