IPC::Message Refactoring: Move POSIX specific bits to PlatformFileAttachment

ipc/ipc_platform_file_attachment_posix.h

Index: ipc/ipc_platform_file_attachment_posix.h
diff --git a/ipc/ipc_platform_file_attachment.h b/ipc/ipc_platform_file_attachment_posix.h
similarity index 60%
rename from ipc/ipc_platform_file_attachment.h
rename to ipc/ipc_platform_file_attachment_posix.h
index c4c22a3c091518f9eca31de7716e9bd98fcae7b5..d1eff609c5340b8c617dcd4a069875121eed1212 100644
--- a/ipc/ipc_platform_file_attachment.h
+++ b/ipc/ipc_platform_file_attachment_posix.h
@@ -5,26 +5,34 @@
 #ifndef IPC_IPC_PLATFORM_FILE_ATTACHMENT_H_
 #define IPC_IPC_PLATFORM_FILE_ATTACHMENT_H_
 
-#include "base/files/file.h"
+#include "ipc/ipc_export.h"
 #include "ipc/ipc_message_attachment.h"
 
 namespace IPC {
 namespace internal {
 
 // A platform file that is sent over |Channel| as a part of |Message|.
-// |PlatformFileAttachment| doesn't own |file_|. The lifecycle of |file_| is
-// managed by |MessageAttachmentSet|.
-class PlatformFileAttachment : public MessageAttachment {
+// PlatformFileAttachment optionally owns the file and |owning_| is set in that
+// case. Also, |file_| is not cleared even after the ownership is taken.
+// Some old clients require this strange behavior.
+class IPC_EXPORT PlatformFileAttachment : public MessageAttachment {
  public:
+  // Non-owning constructor
   explicit PlatformFileAttachment(base::PlatformFile file);
+  // Owning constructor
+  explicit PlatformFileAttachment(base::ScopedFD file);
 
   Type GetType() const override;
+  base::PlatformFile TakePlatformFile() override;
+
   base::PlatformFile file() const { return file_; }
+  bool Owns() const { return owning_.is_valid(); }
 
  private:
   ~PlatformFileAttachment() override;
 
   base::PlatformFile file_;
+  base::ScopedFD owning_;
 };
 
 base::PlatformFile GetPlatformFile(scoped_refptr<MessageAttachment> attachment);