[Sync] Turn notifier::PushClient into an interface

jingle/notifier/listener/notification_defines.h

 // Copyright (c) 2012 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 JINGLE_NOTIFIER_LISTENER_NOTIFICATION_DEFINES_H_
 #define JINGLE_NOTIFIER_LISTENER_NOTIFICATION_DEFINES_H_
 
 #include <string>
 #include <vector>
 
 namespace notifier {
 
 struct Subscription {
+  Subscription();
+  ~Subscription();
+  bool Equals(const Subscription& other) const;
+
   // The name of the channel to subscribe to; usually but not always
   // a URL.
   std::string channel;
   // A sender, which could be a domain or a bare JID, from which we
   // will accept pushes.
   std::string from;
 };
 
 typedef std::vector<Subscription> SubscriptionList;
 
+bool SubscriptionListsEqual(const SubscriptionList& subscriptions1,
+                            const SubscriptionList& subscriptions2);
+
 // A structure representing a <recipient/> block within a push message.
 struct Recipient {
+  Recipient();
+  ~Recipient();
+  bool Equals(const Recipient& other) const;
+
   // The bare jid of the recipient.
   std::string to;
   // User-specific data for the recipient.
   std::string user_specific_data;
 };
 
 typedef std::vector<Recipient> RecipientList;
 
+bool RecipientListsEqual(const RecipientList& recipients1,
+                         const RecipientList& recipients2);
+
 struct Notification {
   Notification();
   ~Notification();
 
   // The channel the notification is coming in on.
   std::string channel;
   // Recipients for this notification (may be empty).
   RecipientList recipients;
   // The notification data payload.
   std::string data;
 
+  bool Equals(const Notification& other) const;
   std::string ToString() const;
 };
 
 }  // namespace notifier
 
 #endif  // JINGLE_NOTIFIER_LISTENER_NOTIFICATION_DEFINES_H_