Revert of Eliminate kMojoChannelToken usage for render processes

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;
 
 struct SerializedHandle {
   handle the_handle;
 
   enum Type {
@@ skipping 14 matching lines @@
   // 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);
 };
-
-// A strictly nominal interface used to identify Channel bootstrap requests.
-interface ChannelBootstrap {};