Support early associated interface binding on ChannelMojo

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 {
     MOJO_HANDLE,
     PLATFORM_FILE,
     WIN_HANDLE,
     MACH_PORT,
   };
 
   Type type;
 };
 
 // A placeholder interface type since we don't yet support generic associated
 // message pipe handles.
 interface GenericInterface {};
 
 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);
 };
-
-// An interface for connecting a pair of Channel interfaces representing a
-// bidirectional IPC channel.
-interface Bootstrap {
-  // Initializes a Chrome IPC channel over |to_client_channel| and
-  // |to_server_channel|. Each side also sends its PID to the other side.
-  Init(associated Channel& to_client_channel,
-       associated Channel to_server_channel,
-       int32 pid) => (int32 pid);
-};