Implements JS bindings for mojo data pipe.

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

Index: third_party/WebKit/Source/core/mojo/MojoWriteDataResult.idl
diff --git a/third_party/WebKit/Source/core/mojo/MojoWriteDataResult.idl b/third_party/WebKit/Source/core/mojo/MojoWriteDataResult.idl
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+// 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 MojoWriteDataResult {
+    required MojoResult result;
+    required unsigned long numBytes;
+};