IPC: Make ChannelReader inherit from SupportsAttachmentBrokering.

ipc/ipc_channel_posix.h

Index: ipc/ipc_channel_posix.h
diff --git a/ipc/ipc_channel_posix.h b/ipc/ipc_channel_posix.h
index 986eb8ae41a32faf3c0f4be040833087c34a718f..879adc3408561e5f108c2e9b70ea9294ee062d01 100644
--- a/ipc/ipc_channel_posix.h
+++ b/ipc/ipc_channel_posix.h
@@ -26,14 +26,18 @@ class IPC_EXPORT ChannelPosix : public Channel,
                                 public internal::ChannelReader,
                                 public base::MessageLoopForIO::Watcher {
  public:
-  ChannelPosix(const IPC::ChannelHandle& channel_handle, Mode mode,
-               Listener* listener);
+  // |broker| must outlive the newly created object.
+  ChannelPosix(const IPC::ChannelHandle& channel_handle,
+               Mode mode,
+               Listener* listener,
+               AttachmentBroker* broker);
   ~ChannelPosix() override;
 
   // Channel implementation
   bool Connect() override;
   void Close() override;
   bool Send(Message* message) override;
+  AttachmentBroker* GetAttachmentBroker() override;
   base::ProcessId GetPeerPID() const override;
   base::ProcessId GetSelfPID() const override;
   int GetClientFileDescriptor() const override;
@@ -175,6 +179,9 @@ class IPC_EXPORT ChannelPosix : public Channel,
   static int global_pid_;
 #endif  // OS_LINUX
 
+  // |broker_| must outlive this instance.
+  AttachmentBroker* broker_;
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(ChannelPosix);
 };