Revert of Make CapabilityFilter be part of Identity

mojo/shell/capability_filter.h

 // 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.
 
 #ifndef MOJO_SHELL_CAPABILITY_FILTER_H_
 #define MOJO_SHELL_CAPABILITY_FILTER_H_
 
 #include <map>
 #include <set>
 
 #include "mojo/public/cpp/bindings/array.h"
 
 namespace mojo {
 namespace shell {
 
-class Identity;
+struct Identity;
 
 // A set of names of interfaces that may be exposed to an application.
 using AllowedInterfaces = std::set<std::string>;
 // A map of allowed applications to allowed interface sets. See shell.mojom for
 // more details.
 using CapabilityFilter = std::map<std::string, AllowedInterfaces>;
 
 // Returns a capability filter that allows an application to connect to any
 // other application and any service exposed by other applications.
 CapabilityFilter GetPermissiveCapabilityFilter();
 
 // Returns the set of interfaces that an application instance with |filter| is
 // allowed to see from an instance with |identity|.
 AllowedInterfaces GetAllowedInterfaces(const CapabilityFilter& filter,
                                        const Identity& identity);
 
 }  // namespace shell
 }  // namespace mojo
 
 
 #endif  // MOJO_SHELL_CAPABILITY_FILTER_H_