IAccessible::get_accChild should only return a descendant.

ui/accessibility/platform/ax_platform_node_win_unittest.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 <oleacc.h>
 
 #include "base/memory/scoped_ptr.h"
 #include "base/win/scoped_bstr.h"
@@ skipping 297 matching lines @@
     ScopedComPtr<IDispatch> result;
     ScopedVariant child2(2);
     ASSERT_EQ(S_OK, root_iaccessible->get_accChild(child2, result.Receive()));
     ASSERT_EQ(result.get(), checkbox_iaccessible);
   }
 
   {
     // Asking for child id 3 should fail.
     ScopedComPtr<IDispatch> result;
     ScopedVariant child3(3);
-    ASSERT_EQ(E_FAIL, root_iaccessible->get_accChild(child3, result.Receive()));
+    ASSERT_EQ(E_INVALIDARG,
+              root_iaccessible->get_accChild(child3, result.Receive()));
   }
 
   // We should be able to ask for the button by its unique id too.
   LONG button_unique_id;
   ScopedComPtr<IAccessible2> button_iaccessible2 =
       ToIAccessible2(button_iaccessible);
   button_iaccessible2->get_uniqueID(&button_unique_id);
   ASSERT_LT(button_unique_id, 0);
   {
     ScopedComPtr<IDispatch> result;
     ScopedVariant button_id_variant(button_unique_id);
     ASSERT_EQ(S_OK, root_iaccessible->get_accChild(button_id_variant,
                                                    result.Receive()));
     ASSERT_EQ(result.get(), button_iaccessible);
   }
 
+  // We shouldn't be able to ask for the root node by its unique ID
+  // from one of its children, though.
+  LONG root_unique_id;
+  ScopedComPtr<IAccessible2> root_iaccessible2 =
+      ToIAccessible2(root_iaccessible);
+  root_iaccessible2->get_uniqueID(&root_unique_id);
+  ASSERT_LT(root_unique_id, 0);
+  {
+    ScopedComPtr<IDispatch> result;
+    ScopedVariant root_id_variant(root_unique_id);
+    ASSERT_EQ(E_INVALIDARG, button_iaccessible->get_accChild(root_id_variant,
+                                                             result.Receive()));
+  }
+
   // Now check parents.
   {
     ScopedComPtr<IDispatch> result;
     ASSERT_EQ(S_OK, button_iaccessible->get_accParent(result.Receive()));
     ASSERT_EQ(result.get(), root_iaccessible);
   }
 
   {
     ScopedComPtr<IDispatch> result;
     ASSERT_EQ(S_OK, checkbox_iaccessible->get_accParent(result.Receive()));
@@ skipping 36 matching lines @@
   ASSERT_EQ(E_FAIL, root_iaccessible2->get_indexInParent(&index));
 
   ASSERT_EQ(S_OK, left_iaccessible2->get_indexInParent(&index));
   EXPECT_EQ(0, index);
 
   ASSERT_EQ(S_OK, right_iaccessible2->get_indexInParent(&index));
   EXPECT_EQ(1, index);
 }
 
 }  // namespace ui