value_cleanup: fixup ListValue::Append() calls that already have a unique_ptr to use.

tools/clang/value_cleanup/tests/list-value-append-expected.cc

 // Copyright 2016 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 <memory>
+
 #include "base/values.h"
 
 #define true true
 
+std::unique_ptr<base::Value> ReturnsUniquePtr() {
+  return nullptr;
+}
+
 void F() {
   base::ListValue list;
   list.AppendBoolean(1 == 0);
   list.AppendBoolean(true);
   list.AppendInteger(static_cast<unsigned char>(1.0));
   list.AppendDouble(double{3});
   list.AppendString("abc");
+
+  list.Append(ReturnsUniquePtr());
+  std::unique_ptr<base::Value> unique_ptr_var;
+  list.Append(std::move(unique_ptr_var));
 }