Make dbus::FileDescriptor a Pass()-movable type.

dbus/file_descriptor.cc

 // Copyright (c) 2012 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/bind.h"
 #include "base/files/file.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/threading/worker_pool.h"
 #include "dbus/file_descriptor.h"
 
 namespace dbus {
 
 void CHROME_DBUS_EXPORT FileDescriptor::Deleter::operator()(
     FileDescriptor* fd) {
   base::WorkerPool::PostTask(
       FROM_HERE, base::Bind(&base::DeletePointer<FileDescriptor>, fd), false);
 }
 
+FileDescriptor::FileDescriptor(RValue other)
+    : value_(other.object->value_),
+      owner_(other.object->owner_),
+      valid_(other.object->valid_) {
+  other.object->value_ = -1;
+  other.object->valid_ = false;
+  other.object->owner_ = false;
+}
+
 FileDescriptor::~FileDescriptor() {
   if (owner_)
     base::File auto_closer(value_);
 }
 
+FileDescriptor& FileDescriptor::operator=(RValue other) {
+  value_ = other.object->value_;

[Alex Vakulenko, 2015/06/10 18:55:47]

I think here you should do just std::swap() on each pair of values.

The current implementation has a problem that if |this| already has some valid
file descriptor set, you'll lose it (without closing).

With swapping, you'd let |other| close the file descriptor if needed.

Alternatively, you'd want to add:

  if (owner_)
    base::File auto_closer(value_);

before assigning a new value from |other|

[Reilly Grant (use Gerrit), 2015/06/10 19:21:10]

Done.

+  owner_ = other.object->owner_;
+  valid_ = other.object->valid_;
+  other.object->value_ = -1;
+  other.object->valid_ = false;
+  other.object->owner_ = false;
+  return *this;
+}
+
 int FileDescriptor::value() const {
   CHECK(valid_);
   return value_;
 }
 
 int FileDescriptor::TakeValue() {
   CHECK(valid_);  // NB: check first so owner_ is unchanged if this triggers
   owner_ = false;
   return value_;
 }
 
 void FileDescriptor::CheckValidity() {
   base::File file(value_);
   base::File::Info info;
   bool ok = file.GetInfo(&info);
   file.TakePlatformFile();  // Prevent |value_| from being closed by |file|.
   valid_ = (ok && !info.is_directory);
 }
 
 }  // namespace dbus