Fix "unused variable" warnings.

content/common/sandbox_linux/bpf_cros_arm_gpu_policy_linux.h

 // Copyright 2013 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 CONTENT_COMMON_SANDBOX_LINUX_BPF_CROS_ARM_GPU_POLICY_LINUX_H_
 #define CONTENT_COMMON_SANDBOX_LINUX_BPF_CROS_ARM_GPU_POLICY_LINUX_H_
 
 #include "base/macros.h"
 #include "content/common/sandbox_linux/bpf_gpu_policy_linux.h"
 
 namespace content {
 
 // This policy is for Chrome OS ARM.
 class CrosArmGpuProcessPolicy : public GpuProcessPolicy {
  public:
   explicit CrosArmGpuProcessPolicy(bool allow_shmat);
   ~CrosArmGpuProcessPolicy() override;
 
   sandbox::bpf_dsl::ResultExpr EvaluateSyscall(
       int system_call_number) const override;
   bool PreSandboxHook() override;
 
  private:
+#if defined(__arm__) || defined(__aarch64__)
   const bool allow_shmat_;  // Allow shmat(2).
+#endif
   DISALLOW_COPY_AND_ASSIGN(CrosArmGpuProcessPolicy);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_COMMON_SANDBOX_LINUX_BPF_CROS_ARM_GPU_POLICY_LINUX_H_