Update from https://crrev.com/316786

sandbox/linux/system_headers/android_ucontext.h

Index: sandbox/linux/system_headers/android_ucontext.h
diff --git a/sandbox/linux/system_headers/android_ucontext.h b/sandbox/linux/system_headers/android_ucontext.h
new file mode 100644
index 0000000000000000000000000000000000000000..8e873bed52171627753621fa651340e1896439ee
--- /dev/null
+++ b/sandbox/linux/system_headers/android_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_ANDROID_UCONTEXT_H_
+#define SANDBOX_LINUX_SYSTEM_HEADERS_ANDROID_UCONTEXT_H_
+
+#if defined(__ANDROID__)
+
+#if defined(__arm__)
+#include "sandbox/linux/system_headers/android_arm_ucontext.h"
+#elif defined(__i386__)
+#include "sandbox/linux/system_headers/android_i386_ucontext.h"
+#elif defined(__x86_64__)
+#include "sandbox/linux/system_headers/android_x86_64_ucontext.h"
+#elif defined(__mips__)
+#include "sandbox/linux/system_headers/android_mips_ucontext.h"
+#elif defined(__aarch64__)
+#include "sandbox/linux/system_headers/android_arm64_ucontext.h"
+#else
+#error "No support for your architecture in Android header"
+#endif
+
+#else  // __ANDROID__
+#error "Android header file included on non Android."
+#endif  // __ANDROID__
+
+#endif  // SANDBOX_LINUX_SYSTEM_HEADERS_ANDROID_UCONTEXT_H_