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

This change:

 * Gets rid of MessageAttachmentSet::owning_descriptors_ by moving
   the responsibility to PlatformFileAttachment, where owning_
   member variable is used to track the lifetime
 * Replaces MessageAttachmetnSet::Add*File() and TakePlatformFile()
   with platform agnostic AddAttachment() and GetAttachmentAt()
 * Repalces Message::ReadFile(), Write*File() with ReadAttachment()
   and WriteAttachmente(), which are also platform agnostic.

This also adds MessageAttachment::TakePlatformFile() virtual function,
which will be implemented by upcoming MojoHandleAttachment as well.

This is another preparation for introducing MojoHandleAttachment,
but it also simplifies Message and MessageAttachmentSet.

R=agl@chromium.org
TBR=mtomasz@chromium.org
BUG=448190

Review URL: https://codereview.chromium.org/883093003

Cr-Commit-Position: refs/heads/master@{#314047}

1 files changed, 43 insertions, 0 deletions

diff --git a/ipc/ipc_platform_file_attachment_posix.h b/ipc/ipc_platform_file_attachment_posix.h
new file mode 100644
index 0000000..d1eff60
--- /dev/null
+++ b/ipc/ipc_platform_file_attachment_posix.h
@@ -0,0 +1,43 @@
+// Copyright (c) 2015 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.
+
+#ifndef IPC_IPC_PLATFORM_FILE_ATTACHMENT_H_
+#define IPC_IPC_PLATFORM_FILE_ATTACHMENT_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 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);
+
+}  // namespace internal
+}  // namespace IPC
+
+#endif  // IPC_IPC_PLATFORM_FILE_ATTACHMENT_H_