Mojo C++ bindings: Simplify associated interface API.

ipc/ipc_channel_mojo.cc

Index: ipc/ipc_channel_mojo.cc
diff --git a/ipc/ipc_channel_mojo.cc b/ipc/ipc_channel_mojo.cc
index c8baa42053dd255293837db860a687f0640fb275..3b4e5e9cab8c003149549c399e58d808b32ebb4d 100644
--- a/ipc/ipc_channel_mojo.cc
+++ b/ipc/ipc_channel_mojo.cc
@@ -399,7 +399,8 @@ ChannelMojo::CreateThreadSafeChannel() {
       task_runner_, base::Bind(&ChannelMojo::ForwardMessageFromThreadSafePtr,
                                weak_factory_.GetWeakPtr()),
       base::Bind(&ChannelMojo::ForwardMessageWithResponderFromThreadSafePtr,
-                 weak_factory_.GetWeakPtr()));
+                 weak_factory_.GetWeakPtr()),
+      *bootstrap_->GetAssociatedGroup());
 }
 
 void ChannelMojo::OnPeerPidReceived(int32_t peer_pid) {