Support generic synchronization against an IPC::Channel

ipc/ipc.mojom

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module IPC.mojom;
 
+import "mojo/common/event.mojom";
+
 // NOTE: This MUST match the value of MSG_ROUTING_NONE in src/ipc/ipc_message.h.
 const int32 kRoutingIdNone = -2;
 
 struct SerializedHandle {
   handle the_handle;
 
   enum Type {
     MOJO_HANDLE,
     PLATFORM_FILE,
     WIN_HANDLE,
@@ skipping 10 matching lines @@
 interface Channel {
   // Informs the remote end of this client's PID. Must be called exactly once,
   // before any calls to Receive() below.
   SetPeerPid(int32 pid);
 
   // Transmits a classical Chrome IPC message.
   Receive(array<uint8> data, array<SerializedHandle>? handles);
 
   // Requests a Channel-associated interface.
   GetAssociatedInterface(string name, associated GenericInterface& request);
+
+  // Signals |event| immediately upon receipt. Useful for synchronizing
+  // arbitrary clients against the Channel's message FIFO.
+  SignalEvent(mojo.common.mojom.Event event);
 };
 
 // A strictly nominal interface used to identify Channel bootstrap requests.
 interface ChannelBootstrap {};