Convert NaCl renderer-loader messages to mojo.

components/nacl/common/nacl.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 nacl.mojom;
+
+[Native]
+enum NaClErrorCode;
+
+interface NaClRendererHost {
+  // This message must be synchronous to ensure that the exit status is sent
+  // from NaCl to the renderer before the NaCl process exits very soon after.
+  [Sync]
+  ReportExitStatus(int32 exit_status) => ();
+
+  // This message must be synchronous to ensure that the load status is sent
+  // from NaCl to the renderer before the NaCl process exits very soon after.
+  [Sync]
+  ReportLoadStatus(NaClErrorCode load_status) => ();
+
+  ProvideExitControl(NaClExitControl exit_control);
+};
+
+// When this interface is closed, it indicates that the NaCl loader process
+// should exit.

[dcheng, 2016/12/20 06:49:54]

Possibly dumb quetion: what's the difference between the NaCl process and the
NaCl loader process?

+interface NaClExitControl {};