Cleanup Tool WebUI: Add browser_proxy javascript class

chrome/browser/resources/cleanup_tool/compiled_resources2.gyp

 # 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.
 {
   'targets': [
     {
+      'target_name': 'cleanup_browser_proxy',
+      'dependencies': [
+        '<(DEPTH)/ui/webui/resources/js/compiled_resources2.gyp:cr',
+      ],
+      'includes': ['../../../../third_party/closure_compiler/compile_js2.gypi'],
+    },
+    {
       'target_name': 'toolbar',
       'dependencies': [
         '<(DEPTH)/ui/webui/resources/js/compiled_resources2.gyp:cr',
       ],
       'includes': ['../../../../third_party/closure_compiler/compile_js2.gypi'],
     },
   ],
 }