Support generic synchronization against an IPC::Channel

ipc/ipc_channel_common.cc

Index: ipc/ipc_channel_common.cc
diff --git a/ipc/ipc_channel_common.cc b/ipc/ipc_channel_common.cc
index 10b88b6de7eee7f3546689a3e956dc07de419399..4ac8ecc08f1190677752e397611a2de610d330f9 100644
--- a/ipc/ipc_channel_common.cc
+++ b/ipc/ipc_channel_common.cc
@@ -67,6 +67,10 @@ Channel::AssociatedInterfaceSupport* Channel::GetAssociatedInterfaceSupport() {
   return nullptr;
 }
 
+void Channel::SendEventToSignal(mojo::common::mojom::EventPtr event) {
+  NOTREACHED();
+}
+
 void Channel::Pause() { NOTREACHED(); }
 
 void Channel::Unpause(bool flush) { NOTREACHED(); }