Mojo JS bindings: draining a DataPipe

mojo/bindings/js/BUILD.gn

 # Copyright 2014 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.
 
 # GYP version: mojo/mojo.gyp:mojo_js_bindings
 source_set("js") {
   sources = [
     "core.cc",
     "core.h",
+    "drain_data.cc",
+    "drain_data.h",
     "handle.cc",
     "handle.h",
     "handle_close_observer.h",
     "support.cc",
     "support.h",
     "waiting_callback.cc",
     "waiting_callback.h",
   ]
 
   public_deps = [
     "//base",
     "//gin",
     "//mojo/common",
     "//v8",
   ]
 }