make base::SharedMemoryHandle a class on POSIX.

base/memory/shared_memory_handle_posix.cc

+// Copyright 2017 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.
+
+#include "base/memory/shared_memory_handle.h"
+
+#include <unistd.h>
+
+#include "base/logging.h"
+#include "base/posix/eintr_wrapper.h"
+
+namespace base {
+
+SharedMemoryHandle::SharedMemoryHandle() = default;
+
+SharedMemoryHandle::SharedMemoryHandle(
+    const base::FileDescriptor& file_descriptor)
+    : file_descriptor(file_descriptor) {}
+

[Nico, 2017/04/27 16:24:44]

do you want to call Close() in the dtor if auto_close is set? (see IMPORTANT
comment in
https://cs.chromium.org/chromium/src/base/file_descriptor_posix.h?q=filedescr...)

[erikchen, 2017/04/27 17:08:10]

No, that's done in ipc_message_utils.cc. 

This CL is a refactor. SharedMemoryHandle is just a wrapper around
FileDescriptor.

+// static
+SharedMemoryHandle SharedMemoryHandle::ImportHandle(int fd) {
+  SharedMemoryHandle handle;
+  handle.file_descriptor.fd = fd;
+  handle.file_descriptor.auto_close = true;
+  return handle;
+}
+
+int SharedMemoryHandle::GetHandle() const {
+  return file_descriptor.fd;
+}
+
+bool SharedMemoryHandle::IsValid() const {
+  return file_descriptor.fd >= 0;
+}
+
+void SharedMemoryHandle::Close() const {
+  if (IGNORE_EINTR(close(file_descriptor.fd)) < 0)
+    PLOG(ERROR) << "close";

[Nico, 2017/04/27 16:24:44]

Should this then call Invalidate()? Closing but keeping an invalid fd around
seems weird.

[erikchen, 2017/04/27 17:08:10]

It should, but it never has on any platform. I've added a TODO in the header and
filed a bug against myself to look into this:
https://bugs.chromium.org/p/chromium/issues/detail?id=716072

+}
+
+void SharedMemoryHandle::Invalidate() {
+  file_descriptor.fd = -1;
+}
+
+SharedMemoryHandle SharedMemoryHandle::Duplicate() const {
+  if (!IsValid())
+    return SharedMemoryHandle();
+
+  int duped_handle = HANDLE_EINTR(dup(file_descriptor.fd));
+  if (duped_handle < 0)
+    return SharedMemoryHandle();
+  return SharedMemoryHandle(FileDescriptor(duped_handle, true));
+}
+
+}  // namespace base