Sync our homegrown SysInfo replacement with the one in Chrome base.

src/base/sys-info.h

+// Copyright 2014 the V8 project 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 V8_BASE_SYS_INFO_H_
+#define V8_BASE_SYS_INFO_H_
+
+#include "include/v8stdint.h"
+#include "src/base/build_config.h"
+
+namespace v8 {
+namespace base {
+
+class SysInfo V8_FINAL {
+ public:
+  // Returns the number of logical processors/core on the current machine.
+  static int NumberOfProcessors();
+
+  // Returns the number of bytes of physical memory on the current machine.
+  static int64_t AmountOfPhysicalMemory();
+
+  // Returns the number of bytes of virtual memory of this process. A return
+  // value of zero means that there is no limit on the available virtual memory.
+  static int64_t AmountOfVirtualMemory();
+};
+
+}  // namespace base
+}  // namespace v8
+
+#endif  // V8_BASE_SYS_INFO_H_