IPC: Make ChannelReader inherit from SupportsAttachmentBrokering.

ipc/ipc_sync_channel.h

 // Copyright (c) 2012 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_SYNC_CHANNEL_H_
 #define IPC_IPC_SYNC_CHANNEL_H_
 
 #include <string>
 #include <deque>
 
@@ skipping 50 matching lines @@
 // message loop pointer to proxy it to the ipc thread.
 class IPC_EXPORT SyncChannel : public ChannelProxy {
  public:
   enum RestrictDispatchGroup {
     kRestrictDispatchGroup_None = 0,
   };
 
   // Creates and initializes a sync channel. If create_pipe_now is specified,
   // the channel will be initialized synchronously.
   // The naming pattern follows IPC::Channel.
+  // TODO(erikchen): Remove default parameter for |broker|. It exists only to
+  // make the upcoming refactor decomposable into smaller CLs.
+  // http://crbug.com/493414.
   static scoped_ptr<SyncChannel> Create(
       const IPC::ChannelHandle& channel_handle,
       IPC::Channel::Mode mode,
       Listener* listener,
       const scoped_refptr<base::SingleThreadTaskRunner>& ipc_task_runner,
       bool create_pipe_now,
-      base::WaitableEvent* shutdown_event);
+      base::WaitableEvent* shutdown_event,
+      AttachmentBroker* broker = nullptr);
 
   static scoped_ptr<SyncChannel> Create(
       scoped_ptr<ChannelFactory> factory,
       Listener* listener,
       const scoped_refptr<base::SingleThreadTaskRunner>& ipc_task_runner,
       bool create_pipe_now,
       base::WaitableEvent* shutdown_event);
 
   // Creates an uninitialized sync channel. Call ChannelProxy::Init to
   // initialize the channel. This two-step setup allows message filters to be
@@ skipping 138 matching lines @@
   // Used to signal events between the IPC and listener threads.
   base::WaitableEventWatcher dispatch_watcher_;
   base::WaitableEventWatcher::EventCallback dispatch_watcher_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncChannel);
 };
 
 }  // namespace IPC
 
 #endif  // IPC_IPC_SYNC_CHANNEL_H_