Revert of ipc: Clean up interface of attachment broker.

ipc/ipc_channel_reader.cc

Index: ipc/ipc_channel_reader.cc
diff --git a/ipc/ipc_channel_reader.cc b/ipc/ipc_channel_reader.cc
index 30f03a1f2decbb2fd74b690baf5cc22eeb392ef5..7e8902e54d2a894a9cfe65df489e3f999c9386c5 100644
--- a/ipc/ipc_channel_reader.cc
+++ b/ipc/ipc_channel_reader.cc
@@ -163,18 +163,9 @@
                IPC_MESSAGE_ID_LINE(m->type()));
 #endif
   m->TraceMessageEnd();
-
-  bool handled = false;
-  if (IsInternalMessage(*m)) {
+  if (IsInternalMessage(*m))
     HandleInternalMessage(*m);
-    handled = true;
-  }
-#if USE_ATTACHMENT_BROKER
-  if (!handled && IsAttachmentBrokerEndpoint() && GetAttachmentBroker()) {
-    handled = GetAttachmentBroker()->OnMessageReceived(*m);
-  }
-#endif  // USE_ATTACHMENT_BROKER
-  if (!handled)
+  else
     listener_->OnMessageReceived(*m);
   if (m->dispatch_error())
     listener_->OnBadMessageReceived(*m);