Adds Mojo IDL.

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

Index: third_party/WebKit/Source/core/mojo/MojoHandle.idl
diff --git a/third_party/WebKit/Source/core/mojo/MojoHandle.idl b/third_party/WebKit/Source/core/mojo/MojoHandle.idl
new file mode 100644
index 0000000000000000000000000000000000000000..34b1dfc97eec0b9fdfba22eb17b66a65d9ac1fdb
--- /dev/null
+++ b/third_party/WebKit/Source/core/mojo/MojoHandle.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.
+
+callback MojoWatchCallback = void (MojoResult result);
+
+[
+    RuntimeEnabled=MojoJS,
+] interface MojoHandle {
+    void close();
+    [CallWith=ScriptState] MojoWatcher watch(MojoHandleSignals signals, MojoWatchCallback callback);
+    MojoResult writeMessage(BufferSource buffer, sequence<MojoHandle> handles);
+    MojoReadMessageResult readMessage(optional MojoReadMessageFlags flags);
+};