IPC: Make ChannelReader inherit from SupportsAttachmentBrokering.

ipc/ipc_channel_proxy.h

Index: ipc/ipc_channel_proxy.h
diff --git a/ipc/ipc_channel_proxy.h b/ipc/ipc_channel_proxy.h
index 5d38006b5d5854f5749c38e0ac956b5077046e26..73cb7e023ee79a2332eff7285348effd40d863f0 100644
--- a/ipc/ipc_channel_proxy.h
+++ b/ipc/ipc_channel_proxy.h
@@ -82,11 +82,15 @@ class IPC_EXPORT ChannelProxy : public Sender, public base::NonThreadSafe {
   // on the background thread.  Any message not handled by the filter will be
   // dispatched to the listener.  The given task runner correspond to a thread
   // on which IPC::Channel is created and used (e.g. IO thread).
+  // 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<ChannelProxy> Create(
       const IPC::ChannelHandle& channel_handle,
       Channel::Mode mode,
       Listener* listener,
-      const scoped_refptr<base::SingleThreadTaskRunner>& ipc_task_runner);
+      const scoped_refptr<base::SingleThreadTaskRunner>& ipc_task_runner,
+      AttachmentBroker* broker = nullptr);
 
   static scoped_ptr<ChannelProxy> Create(
       scoped_ptr<ChannelFactory> factory,
@@ -99,8 +103,13 @@ class IPC_EXPORT ChannelProxy : public Sender, public base::NonThreadSafe {
   // proxy that was not initialized in its constructor. If create_pipe_now is
   // true, the pipe is created synchronously. Otherwise it's created on the IO
   // thread.
-  void Init(const IPC::ChannelHandle& channel_handle, Channel::Mode mode,
-            bool create_pipe_now);
+  // TODO(erikchen): Remove default parameter for |broker|. It exists only to
+  // make the upcoming refactor decomposable into smaller CLs.
+  // http://crbug.com/493414.
+  void Init(const IPC::ChannelHandle& channel_handle,
+            Channel::Mode mode,
+            bool create_pipe_now,
+            AttachmentBroker* broker = nullptr);
   void Init(scoped_ptr<ChannelFactory> factory, bool create_pipe_now);
 
   // Close the IPC::Channel.  This operation completes asynchronously, once the