Re-land Move ScopedFileDescriptor to dbus/file_descriptor.h

dbus/file_descriptor.h

Index: dbus/file_descriptor.h
diff --git a/dbus/file_descriptor.h b/dbus/file_descriptor.h
index 19e0b1ab44b32da4b419a5bef30fbcc4cb386a75..a01ee6ee0115815a951fd5b9005adbf7445bdd2a 100644
--- a/dbus/file_descriptor.h
+++ b/dbus/file_descriptor.h
@@ -6,6 +6,7 @@
 #define DBUS_FILE_DESCRIPTOR_H_
 
 #include "base/basictypes.h"
+#include "base/memory/scoped_ptr.h"
 #include "dbus/dbus_export.h"
 
 namespace dbus {
@@ -33,6 +34,12 @@ namespace dbus {
 // with i/o restrictions.
 class CHROME_DBUS_EXPORT FileDescriptor {
  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.
+  struct Deleter {
+    void CHROME_DBUS_EXPORT operator()(FileDescriptor* fd);
+  };
+
   // Permits initialization without a value for passing to
   // dbus::MessageReader::PopFileDescriptor to fill in and from int values.
   FileDescriptor() : value_(-1), owner_(false), valid_(false) {}
@@ -70,6 +77,9 @@ class CHROME_DBUS_EXPORT FileDescriptor {
   DISALLOW_COPY_AND_ASSIGN(FileDescriptor);
 };
 
+using ScopedFileDescriptor =
+    scoped_ptr<FileDescriptor, FileDescriptor::Deleter>;
+
 }  // namespace dbus
 
 #endif  // DBUS_FILE_DESCRIPTOR_H_