Create a fresh sync datatype for Synced Notifications

sync/protocol/synced_notification_specifics.proto

Index: sync/protocol/synced_notification_specifics.proto
diff --git a/sync/protocol/preference_specifics.proto b/sync/protocol/synced_notification_specifics.proto
similarity index 64%
copy from sync/protocol/preference_specifics.proto
copy to sync/protocol/synced_notification_specifics.proto
index 4827c5dc20ceba8b127ce45bb52d0d7ee6f9c0d5..db82f525ee49b42eb0a102a87235da0c026c47f1 100644
--- a/sync/protocol/preference_specifics.proto
+++ b/sync/protocol/synced_notification_specifics.proto
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
-// Sync protocol datatype extension for preferences.
+// Sync protocol datatype extension for synced notifications.
 
 // Update proto_value_conversions{.h,.cc,_unittest.cc} if you change
 // any fields in this file.
@@ -14,9 +14,7 @@ option retain_unknown_fields = true;
 
 package sync_pb;
 
-// Properties of preference sync objects.
-message PreferenceSpecifics {
-  optional string name = 1;
-  optional string value = 2;
+// Properties of SyncedNotificationSpecifics objects.
+message SyncedNotificationSpecifics {
+  // TODO(petewil): this is placeholder data, make a real one
 }
-