Migrate BrowserAccessibility windows unique id handling to AXPlatformNodeWin.

content/browser/accessibility/browser_accessibility_win.cc

Index: content/browser/accessibility/browser_accessibility_win.cc
diff --git a/content/browser/accessibility/browser_accessibility_win.cc b/content/browser/accessibility/browser_accessibility_win.cc
index 7e9341c5e0baf26a9175dd035ef43868e3d4d754..c013b958f20844521df6dab473b3d7a96b1bc2b4 100644
--- a/content/browser/accessibility/browser_accessibility_win.cc
+++ b/content/browser/accessibility/browser_accessibility_win.cc
@@ -4,7 +4,7 @@
 
 #include "content/browser/accessibility/browser_accessibility_win.h"
 #include "content/browser/accessibility/browser_accessibility_manager.h"
-
+#include "ui/accessibility/platform/ax_platform_node_base.h"
 #include "ui/base/win/atl_module.h"
 
 namespace content {
@@ -43,6 +43,10 @@ void BrowserAccessibilityWin::OnSubtreeWillBeDeleted() {
   GetCOM()->FireNativeEvent(EVENT_OBJECT_HIDE);
 }
 
+int32_t BrowserAccessibilityWin::unique_id() const {
+  return GetCOM()->unique_id();
+}
+
 bool BrowserAccessibilityWin::IsNative() const {
   return true;
 }