Add more GN deps to the build.

third_party/dom_distiller_js/dom_distiller_js.gyp

 # 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.
 {
     'targets': [
         {
+            # GN version: //third_party/dom_distiller_js:proto
             'target_name': 'dom_distiller_js_proto',
             'type': 'static_library',
             'sources': [ 'package/proto/dom_distiller.proto', ],
             'variables': {
               'proto_in_dir': 'package/proto',
               'proto_out_dir': 'third_party/dom_distiller_js',
             },
             'direct_dependent_settings': {
               'include_dirs': ['package/proto_gen'],
             },
             'includes': [ '../../build/protoc.gypi', ],
         }
     ]
 }