Adds Mojo IDL.

third_party/WebKit/Source/core/mojo/MojoReadMessageResult.idl

Index: third_party/WebKit/Source/core/mojo/MojoReadMessageResult.idl
diff --git a/third_party/WebKit/Source/core/mojo/MojoReadMessageResult.idl b/third_party/WebKit/Source/core/mojo/MojoReadMessageResult.idl
new file mode 100644
index 0000000000000000000000000000000000000000..f08503cd8f4951c2a3e01b6951b593a8f775b6f0
--- /dev/null
+++ b/third_party/WebKit/Source/core/mojo/MojoReadMessageResult.idl
@@ -0,0 +1,14 @@
+// Copyright 2017 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.
+
+dictionary MojoReadMessageResult {
+  // TODO(alokp): Consider raising exception for read error.
+  required MojoResult result;
+
+  // TODO(alokp): Check if returning DataView makes sense.
+  // It would require some changes in mojo/js/public/[buffer,codec].js.
+  ArrayBuffer buffer;
+
+  sequence<MojoHandle> handles;
+};