Makes ViewManagerServiceImpl track a single root

mojo/services/view_manager/access_policy_delegate.h

 // 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.
 
 #ifndef MOJO_SERVICES_VIEW_MANAGER_ACCESS_POLICY_DELEGATE_H_
 #define MOJO_SERVICES_VIEW_MANAGER_ACCESS_POLICY_DELEGATE_H_
 
 #include <vector>
 
 #include "base/containers/hash_tables.h"
 #include "mojo/services/view_manager/ids.h"
 
 namespace mojo {
 namespace service {
 
 class ServerView;
 
 // Delegate used by the AccessPolicy implementations to get state.
 class AccessPolicyDelegate {
  public:
-  // Returns the ids of the roots views for this connection. That is, this is
-  // the set of views the connection was embedded at.
-  virtual const base::hash_set<Id>& GetRootsForAccessPolicy() const = 0;
+  // Returns true if |id| is the root of the connection.
+  virtual bool IsRootForAccessPolicy(const ViewId& id) const = 0;
 
   // Returns true if |view| has been exposed to the client.
   virtual bool IsViewKnownForAccessPolicy(const ServerView* view) const = 0;
 
   // Returns true if Embed(view) has been invoked on |view|.
   virtual bool IsViewRootOfAnotherConnectionForAccessPolicy(
       const ServerView* view) const = 0;
 
  protected:
   virtual ~AccessPolicyDelegate() {}
 };
 
 }  // namespace service
 }  // namespace mojo
 
 #endif  // MOJO_SERVICES_VIEW_MANAGER_ACCESS_POLICY_DELEGATE_H_