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

This will make it possible to return a dbus::FileDescriptor from a
function and bind it to a callback without wrapping it in a
dbus::ScopedFileDescriptor. This will allow us to fix the generated
DBus bindings to support methods that have file descriptors as output
parameters.

BUG=496469

Review URL: https://codereview.chromium.org/1170283005

Cr-Commit-Position: refs/heads/master@{#333901}

2 files changed, 31 insertions, 2 deletions

diff --git a/dbus/file_descriptor.cc b/dbus/file_descriptor.cc
index e607fc0..c67a9e1 100644
--- a/dbus/file_descriptor.cc
+++ b/dbus/file_descriptor.cc
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include <algorithm>
+
 #include "base/bind.h"
 #include "base/files/file.h"
 #include "base/location.h"
@@ -9,6 +11,8 @@
 #include "base/threading/worker_pool.h"
 #include "dbus/file_descriptor.h"
 
+using std::swap;
+
 namespace dbus {
 
 void CHROME_DBUS_EXPORT FileDescriptor::Deleter::operator()(
@@ -17,11 +21,21 @@ void CHROME_DBUS_EXPORT FileDescriptor::Deleter::operator()(
       FROM_HERE, base::Bind(&base::DeletePointer<FileDescriptor>, fd), false);
 }
 
+FileDescriptor::FileDescriptor(RValue other)
+    : value_(-1), owner_(false), valid_(false) {
+  Swap(other.object);
+}
+
 FileDescriptor::~FileDescriptor() {
   if (owner_)
     base::File auto_closer(value_);
 }
 
+FileDescriptor& FileDescriptor::operator=(RValue other) {
+  Swap(other.object);
+  return *this;
+}
+
 int FileDescriptor::value() const {
   CHECK(valid_);
   return value_;
@@ -41,4 +55,10 @@ void FileDescriptor::CheckValidity() {
   valid_ = (ok && !info.is_directory);
 }
 
+void FileDescriptor::Swap(FileDescriptor* other) {
+  swap(value_, other->value_);
+  swap(owner_, other->owner_);
+  swap(valid_, other->valid_);
+}
+
 }  // namespace dbus
diff --git a/dbus/file_descriptor.h b/dbus/file_descriptor.h
index a01ee6e..8a41097 100644
--- a/dbus/file_descriptor.h
+++ b/dbus/file_descriptor.h
@@ -7,6 +7,7 @@
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/move.h"
 #include "dbus/dbus_export.h"
 
 namespace dbus {
@@ -33,6 +34,8 @@ namespace dbus {
 // also allows the caller to do this work on the File thread to conform
 // with i/o restrictions.
 class CHROME_DBUS_EXPORT FileDescriptor {
+  MOVE_ONLY_TYPE_FOR_CPP_03(FileDescriptor, RValue);
+
  public:
   // This provides a simple way to pass around file descriptors since they must
   // be closed on a thread that is allowed to perform I/O.
@@ -46,8 +49,14 @@ class CHROME_DBUS_EXPORT FileDescriptor {
   explicit FileDescriptor(int value) : value_(value), owner_(false),
       valid_(false) {}
 
+  // Move constructor for C++03 move emulation of this type.
+  FileDescriptor(RValue other);
+
   virtual ~FileDescriptor();
 
+  // Move operator= for C++03 move emulation of this type.
+  FileDescriptor& operator=(RValue other);
+
   // Retrieves value as an int without affecting ownership.
   int value() const;
 
@@ -70,11 +79,11 @@ class CHROME_DBUS_EXPORT FileDescriptor {
   void CheckValidity();
 
  private:
+  void Swap(FileDescriptor* other);
+
   int value_;
   bool owner_;
   bool valid_;
-
-  DISALLOW_COPY_AND_ASSIGN(FileDescriptor);
 };
 
 using ScopedFileDescriptor =