Revise InterfaceRegistry API to support filtering interfaces @ Bind() time.

services/service_manager/public/cpp/identity.h

 // 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.
 
 #ifndef SERVICES_SERVICE_MANAGER_PUBLIC_CPP_IDENTITY_H_
 #define SERVICES_SERVICE_MANAGER_PUBLIC_CPP_IDENTITY_H_
 
 #include <string>
 
 namespace service_manager {
 
 // Represents the identity of an application.
 // |name| is the structured name of the application.
 // |instance| is a string that allows to tie a specific instance to another. A
 // typical use case of instance is to control process grouping for a given name.
 class Identity {
  public:
   Identity();
   Identity(const std::string& name,
            const std::string& user_id);
   Identity(const std::string& name,
            const std::string& user_id,
            const std::string& instance);
   Identity(const Identity& other);
   ~Identity();
 
   bool operator<(const Identity& other) const;
-  bool is_null() const { return name_.empty(); }
   bool operator==(const Identity& other) const;
+  bool IsValid() const;
 
   const std::string& name() const { return name_; }
   const std::string& user_id() const { return user_id_; }
   void set_user_id(const std::string& user_id) { user_id_ = user_id; }
   const std::string& instance() const { return instance_; }
 
  private:
   std::string name_;
   std::string user_id_;
   std::string instance_;
 };
 
 }  // namespace service_manager
 
 #endif  // SERVICES_SERVICE_MANAGER_PUBLIC_CPP_IDENTITY_H_