Add module suffix in .mojom files for components/arc

components/arc/common/policy.mojom

 // Copyright 2016 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.
 
-module arc;
+module arc.mojom;
 
 interface PolicyHost {
   // Get policies from Chrome OS, as JSON-encoded dictionary with the policies'
   // names as keys and their values as values. The list of possible policies can
   // be found in components/policy/resources/policy_templates.json
   GetPolicies@0() => (string policies);
 };
 
 interface PolicyInstance {
   // Establishes full-duplex communication with the host.
   Init@0(PolicyHost host_ptr);
 
   // Indicates some policies have changed
   OnPolicyUpdated@1();
 };