Adds Mojo IDL.

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

Index: third_party/WebKit/Source/core/mojo/MojoHandleSignals.idl
diff --git a/third_party/WebKit/Source/core/mojo/MojoHandleSignals.idl b/third_party/WebKit/Source/core/mojo/MojoHandleSignals.idl
new file mode 100644
index 0000000000000000000000000000000000000000..fe0f02d30c3dbb3d5b52e30060af0ec5b793278f
--- /dev/null
+++ b/third_party/WebKit/Source/core/mojo/MojoHandleSignals.idl
@@ -0,0 +1,9 @@
+// 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 MojoHandleSignals {
+  boolean readable = false;
+  boolean writable = false;
+  boolean peerClosed = false;
+};