Forward BrowserAccessibilityWin::get_accHelp to the platform node.

ui/accessibility/platform/ax_platform_node_win.cc

Index: ui/accessibility/platform/ax_platform_node_win.cc
diff --git a/ui/accessibility/platform/ax_platform_node_win.cc b/ui/accessibility/platform/ax_platform_node_win.cc
index 9aa621d744534c20dd673fb7bb182d82566a2a4c..4da305dd8a5f8212408b97ba41c8a00ef8611ebd 100644
--- a/ui/accessibility/platform/ax_platform_node_win.cc
+++ b/ui/accessibility/platform/ax_platform_node_win.cc
@@ -509,6 +509,7 @@ STDMETHODIMP AXPlatformNodeWin::get_accState(
 
 STDMETHODIMP AXPlatformNodeWin::get_accHelp(
     VARIANT var_id, BSTR* help) {
+  COM_OBJECT_VALIDATE_1_ARG(help);
   return S_FALSE;
 }