Restore aura support from Mojo repo.

mandoline/BUILD.gn

 # Copyright 2015 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.
 
 group("mandoline") {
   # Meta-target, don't link into production code.
   testonly = true
 
   # TODO(beng): should be able to remove this in favor of explicit dependencies
   #             from subdirs.
   deps = [
+    "//mandoline/ui",
     "//mojo",
   ]
 
   if (!is_component_build) {
     deps += [ "//mandoline/app" ]
   }
 }