[Sync] Add support for server controlled nudge delays

sync/sessions/sync_session.h

Index: sync/sessions/sync_session.h
diff --git a/sync/sessions/sync_session.h b/sync/sessions/sync_session.h
index d61a7920f0826577c0049b41bf99b3f4f9189a8a..a565f563bde8da1a7a5f9598f85154e410428ac8 100644
--- a/sync/sessions/sync_session.h
+++ b/sync/sessions/sync_session.h
@@ -71,10 +71,9 @@ class SYNC_EXPORT_PRIVATE SyncSession {
     virtual void OnReceivedLongPollIntervalUpdate(
         const base::TimeDelta& new_interval) = 0;
 
-    // The client has been instructed to change its sessions commit
-    // delay.
-    virtual void OnReceivedSessionsCommitDelay(
-        const base::TimeDelta& new_delay) = 0;
+    // The client has been instructed to change a nudge delay.
+    virtual void OnReceivedCustomNudgeDelays(
+        const std::map<ModelType, int>& nudge_delays) = 0;
 
     // Called for the syncer to respond to the error sent by the server.
     virtual void OnSyncProtocolError(