Update from https://crrev.com/327068

sandbox/linux/system_headers/linux_ucontext.h

Index: sandbox/linux/system_headers/linux_ucontext.h
diff --git a/sandbox/linux/system_headers/linux_ucontext.h b/sandbox/linux/system_headers/linux_ucontext.h
new file mode 100644
index 0000000000000000000000000000000000000000..ea4d8a6c1fd58c2fa8841fb5e5609c77b7389d34
--- /dev/null
+++ b/sandbox/linux/system_headers/linux_ucontext.h
@@ -0,0 +1,28 @@
+// Copyright (c) 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 SANDBOX_LINUX_SYSTEM_HEADERS_LINUX_UCONTEXT_H_
+#define SANDBOX_LINUX_SYSTEM_HEADERS_LINUX_UCONTEXT_H_
+
+#if defined(__ANDROID__) || defined(__native_client_nonsfi__)
+
+#if defined(__arm__)
+#include "sandbox/linux/system_headers/arm_linux_ucontext.h"
+#elif defined(__i386__)
+#include "sandbox/linux/system_headers/i386_linux_ucontext.h"
+#elif defined(__x86_64__)
+#include "sandbox/linux/system_headers/x86_64_linux_ucontext.h"
+#elif defined(__mips__)
+#include "sandbox/linux/system_headers/mips_linux_ucontext.h"
+#elif defined(__aarch64__)
+#include "sandbox/linux/system_headers/arm64_linux_ucontext.h"
+#else
+#error "No support for your architecture in Android or PNaCl header"
+#endif
+
+#else  // defined(__ANDROID__) || defined(__native_client_nonsfi__)
+#error "The header file included on non Android and non PNaCl."
+#endif  // defined(__ANDROID__) || defined(__native_client_nonsfi__)
+
+#endif  // SANDBOX_LINUX_SYSTEM_HEADERS_LINUX_UCONTEXT_H_