Mojo C++ bindings: support disconnect with a reason.

mojo/public/interfaces/bindings/interface_control_messages.mojom

 // Copyright 2015 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.
 
 [JavaPackage="org.chromium.mojo.bindings.interfacecontrol"]
 module mojo.interface_control;
 
-// For each user-defined interface, some control functions are provided at the
-// same end of the message pipe as the user-defined interface, providing
-// information about the user-defined interface.
+// For each user-defined interface, some control functions are provided by the
+// interface endpoints at both sides.
 
 ////////////////////////////////////////////////////////////////////////////////
 // Run@0xFFFFFFFF(RunInput input) => (RunOutput? output);
 //
 // This control function runs the input command. If the command is not
 // supported, |output| is set to null; otherwise |output| stores the result,
 // whose type depends on the input.
 
 const uint32 kRunMessageId = 0xFFFFFFFF;
 
 struct RunMessageParams {
   RunInput input;
 };
 union RunInput {
   QueryVersion query_version;
   FlushForTesting flush_for_testing;
 };
 
 struct RunResponseMessageParams {
   RunOutput? output;
 };
 union RunOutput {
   QueryVersionResult query_version_result;
 };
 
 // Queries the max supported version of the user-defined interface.
+// Sent by the interface client side.
 struct QueryVersion {
 };
 struct QueryVersionResult {
   uint32 version;
 };
 
+// Sent by either side of the interface.
 struct FlushForTesting {
 };
 
 ////////////////////////////////////////////////////////////////////////////////
 // RunOrClosePipe@0xFFFFFFFE(RunOrClosePipeInput input);
 //
 // This control function runs the input command. If the operation fails or the
 // command is not supported, the message pipe is closed.
 
 const uint32 kRunOrClosePipeMessageId = 0xFFFFFFFE;
 
 struct RunOrClosePipeMessageParams {
   RunOrClosePipeInput input;
 };
 union RunOrClosePipeInput {
   RequireVersion require_version;
+  SendDisconnectReason send_disconnect_reason;
 };
 
 // If the specified version of the user-defined interface is not supported, the
 // function fails and the pipe is closed.
+// Sent by the interface client side.
 struct RequireVersion {
   uint32 version;
 };
+
+// A user-defined reason about why the interface is disconnected. The sender
+// usually send this message and immediately disconnect the interface.
+// Sent by either side of the interface.
+struct SendDisconnectReason {
+  uint32 custom_reason;
+  string description;
+};