[Sync] Turn notifier::PushClient into an interface

jingle/notifier/listener/push_client_observer.h

Index: jingle/notifier/listener/push_client_observer.h
diff --git a/jingle/notifier/listener/push_client_observer.h b/jingle/notifier/listener/push_client_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..0fe7d467295746bca2689611847c06a7cd4575eb
--- /dev/null
+++ b/jingle/notifier/listener/push_client_observer.h
@@ -0,0 +1,32 @@
+// 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_NON_BLOCKING_PUSH_CLIENT_OBSERVER_H_
+#define JINGLE_NOTIFIER_LISTENER_NON_BLOCKING_PUSH_CLIENT_OBSERVER_H_
+
+#include "jingle/notifier/listener/notification_defines.h"
+
+namespace notifier {
+
+// A PushClientObserver is notified whenever an incoming notification
+// is received or when the state of the push client changes.
+class PushClientObserver {
+ protected:
+  virtual ~PushClientObserver();
+
+ public:
+  // Called when the state of the push client changes.  If
+  // |notifications_enabled| is true, that means notifications can be
+  // sent and received freely.  If it is false, that means no
+  // notifications can be sent or received.
+  virtual void OnNotificationStateChange(bool notifications_enabled) = 0;
+
+  // Called when a notification is received.  The details of the
+  // notification are in |notification|.
+  virtual void OnIncomingNotification(const Notification& notification) = 0;
+};
+
+}  // namespace notifier
+
+#endif  // JINGLE_NOTIFIER_LISTENER_NON_BLOCKING_PUSH_CLIENT_OBSERVER_H_