Forward BrowserAccessibilityWin::get_accHelp to the platform node.

ui/accessibility/platform/ax_platform_node_win.cc

 // Copyright 2015 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.
 
 #include <atlbase.h>
 #include <atlcom.h>
 #include <limits.h>
 #include <oleacc.h>
 #include <stdint.h>
 
@@ skipping 491 matching lines @@
     VARIANT var_id, VARIANT* state) {
   AXPlatformNodeWin* target;
   COM_OBJECT_VALIDATE_VAR_ID_1_ARG_AND_GET_TARGET(var_id, state, target);
   state->vt = VT_I4;
   state->lVal = target->MSAAState();
   return S_OK;
 }
 
 STDMETHODIMP AXPlatformNodeWin::get_accHelp(
     VARIANT var_id, BSTR* help) {
+  COM_OBJECT_VALIDATE_1_ARG(help);
   return S_FALSE;
 }
 
 STDMETHODIMP AXPlatformNodeWin::get_accValue(VARIANT var_id, BSTR* value) {
   AXPlatformNodeWin* target;
   COM_OBJECT_VALIDATE_VAR_ID_1_ARG_AND_GET_TARGET(var_id, value, target);
   return target->GetStringAttributeAsBstr(ui::AX_ATTR_VALUE, value);
 }
 
 STDMETHODIMP AXPlatformNodeWin::put_accValue(VARIANT var_id,
@@ skipping 759 matching lines @@
 
   AXPlatformNodeBase* base =
       FromNativeViewAccessible(node->GetNativeViewAccessible());
   if (base && !IsDescendant(base))
     base = nullptr;
 
   return static_cast<AXPlatformNodeWin*>(base);
 }
 
 }  // namespace ui