IPC: Remove unnecessary conversions of BrokerableAttachment.

ipc/ipc_channel_reader_unittest.cc

Index: ipc/ipc_channel_reader_unittest.cc
diff --git a/ipc/ipc_channel_reader_unittest.cc b/ipc/ipc_channel_reader_unittest.cc
index c528996b4245d331059ca2aa740bab0f863b6c33..fdf31446b005bb464cc3c0928512a3c630686b28 100644
--- a/ipc/ipc_channel_reader_unittest.cc
+++ b/ipc/ipc_channel_reader_unittest.cc
@@ -42,8 +42,9 @@ class MockAttachmentBroker : public AttachmentBroker {
  public:
   typedef std::set<scoped_refptr<BrokerableAttachment>> AttachmentSet;
 
-  bool SendAttachmentToProcess(BrokerableAttachment* attachment,
-                               base::ProcessId destination_process) override {
+  bool SendAttachmentToProcess(
+      const scoped_refptr<BrokerableAttachment>& attachment,
+      base::ProcessId destination_process) override {
     return false;
   }