IPC: Make ChannelReader inherit from SupportsAttachmentBrokering.

ipc/ipc_channel_nacl.h

Index: ipc/ipc_channel_nacl.h
diff --git a/ipc/ipc_channel_nacl.h b/ipc/ipc_channel_nacl.h
index f0649b2602228a8670b91bff3e3870fc2fb08a16..a9d2139ca38c66eab991c3bd1cdd99f82f3cd97b 100644
--- a/ipc/ipc_channel_nacl.h
+++ b/ipc/ipc_channel_nacl.h
@@ -37,7 +37,8 @@ class ChannelNacl : public Channel,
   // Mirror methods of Channel, see ipc_channel.h for description.
   ChannelNacl(const IPC::ChannelHandle& channel_handle,
               Mode mode,
-              Listener* listener);
+              Listener* listener,
+              AttachmentBroker* broker);
   ~ChannelNacl() override;
 
   // Channel implementation.
@@ -46,6 +47,7 @@ class ChannelNacl : public Channel,
   bool Connect() override;
   void Close() override;
   bool Send(Message* message) override;
+  AttachmentBroker* GetAttachmentBroker() override;
 
   // Posted to the main thread by ReaderThreadRunner.
   void DidRecvMsg(scoped_ptr<MessageContents> contents);
@@ -114,6 +116,9 @@ class ChannelNacl : public Channel,
 
   base::WeakPtrFactory<ChannelNacl> weak_ptr_factory_;
 
+  // |broker_| must outlive this instance.

[Tom Sepez, 2015/06/16 16:36:44]

nit: maybe move this comment to the ctor, where the caller will actually pass in
the broker.

[erikchen, 2015/06/16 17:36:47]

I kept the comment here, and added a similar comment to the constructor. 

+  AttachmentBroker* broker_;

[Will Harris, 2015/06/16 13:06:04]

where will this object be created and how will the lifetime be managed, all the
code in this CL passes nullptr so hard to determine.

[erikchen, 2015/06/16 17:36:47]

The short answer is: Each process is responsible for ensuring the lifetime of
this object, and in general this is one of the last objects to be deleted when a
process is destroyed.

The long answer is: See this CL: https://codereview.chromium.org/1184523003/ for
more context. The CL I referenced is not going to go out for review (since it
touches ~50 files), and this CL that you're currently reviewing is a strict
subset of this CL.

+
   DISALLOW_IMPLICIT_CONSTRUCTORS(ChannelNacl);
 };