[Sync] Turn notifier::PushClient into an interface

jingle/notifier/listener/notification_defines.h

Index: jingle/notifier/listener/notification_defines.h
diff --git a/jingle/notifier/listener/notification_defines.h b/jingle/notifier/listener/notification_defines.h
index f85288fe505ea86aa136dd58c3c9666bbf0b342b..5d4a0c83dc1c6603ad3077a5c4963ff3f115a6fb 100644
--- a/jingle/notifier/listener/notification_defines.h
+++ b/jingle/notifier/listener/notification_defines.h
@@ -11,6 +11,10 @@
 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;
@@ -21,8 +25,15 @@ struct Subscription {
 
 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.
@@ -31,6 +42,9 @@ struct Recipient {
 
 typedef std::vector<Recipient> RecipientList;
 
+bool RecipientListsEqual(const RecipientList& recipients1,
+                         const RecipientList& recipients2);
+
 struct Notification {
   Notification();
   ~Notification();
@@ -42,6 +56,7 @@ struct Notification {
   // The notification data payload.
   std::string data;
 
+  bool Equals(const Notification& other) const;
   std::string ToString() const;
 };