clang/win: Fix build after https://codereview.chromium.org/1456663003

sandbox/win/src/sandbox_policy_base.h

 // Copyright (c) 2011 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.
 
 #ifndef SANDBOX_WIN_SRC_SANDBOX_POLICY_BASE_H_
 #define SANDBOX_WIN_SRC_SANDBOX_POLICY_BASE_H_
 
 #include <windows.h>
 
 #include <list>
@@ skipping 14 matching lines @@
 
 namespace sandbox {
 
 class AppContainerAttributes;
 class LowLevelPolicy;
 class TargetProcess;
 struct PolicyGlobal;
 
 typedef std::vector<base::win::ScopedHandle*> HandleList;
 
-class PolicyBase : public TargetPolicy {
+class PolicyBase final : public TargetPolicy {
  public:
   PolicyBase();
 
   // TargetPolicy:
   void AddRef() override;
   void Release() override;
   ResultCode SetTokenLevel(TokenLevel initial, TokenLevel lockdown) override;
   TokenLevel GetInitialTokenLevel() const override;
   TokenLevel GetLockdownTokenLevel() const override;
   ResultCode SetJobLevel(JobLevel job_level, uint32 ui_exceptions) override;
@@ skipping 120 matching lines @@
   // This list contains handles other than the stderr/stdout handles which are
   // shared with the target at times.
   HandleList handles_to_share_;
 
   DISALLOW_COPY_AND_ASSIGN(PolicyBase);
 };
 
 }  // namespace sandbox
 
 #endif  // SANDBOX_WIN_SRC_SANDBOX_POLICY_BASE_H_