Migrate BrowserAccessibility windows unique id handling to AXPlatformNodeWin.

content/browser/accessibility/browser_accessibility_manager_win.cc

Index: content/browser/accessibility/browser_accessibility_manager_win.cc
diff --git a/content/browser/accessibility/browser_accessibility_manager_win.cc b/content/browser/accessibility/browser_accessibility_manager_win.cc
index bc7c07475474f88bbe50482c4f821f9a4d33c42c..8ca0562b442a1523037bbd513bf4fd853936824e 100644
--- a/content/browser/accessibility/browser_accessibility_manager_win.cc
+++ b/content/browser/accessibility/browser_accessibility_manager_win.cc
@@ -202,7 +202,7 @@ BrowserAccessibilityEvent::Result
   // argument to NotifyWinEvent; the AT client will then call get_accChild
   // on the HWND's accessibility object and pass it that same id, which
   // we can use to retrieve the IAccessible for this node.
-  LONG child_id = -target->unique_id();
+  LONG child_id = -(ToBrowserAccessibilityWin(target)->GetCOM()->unique_id());
   ::NotifyWinEvent(win_event_type, hwnd, OBJID_CLIENT, child_id);
   return BrowserAccessibilityEvent::Sent;
 }