Server directed error handling backend code.

chrome/browser/sync/sessions/sync_session.h

Index: chrome/browser/sync/sessions/sync_session.h
diff --git a/chrome/browser/sync/sessions/sync_session.h b/chrome/browser/sync/sessions/sync_session.h
index 9520f9dcfe65515245cde396d429a24049bb4eb4..04b1a1a15b06104e0106e7f2cc8d1307aba2b85b 100644
--- a/chrome/browser/sync/sessions/sync_session.h
+++ b/chrome/browser/sync/sessions/sync_session.h
@@ -79,8 +79,17 @@ class SyncSession {
     // the Syncer detects that the backend store has fundamentally changed or
     // is a different instance altogether (e.g. swapping from a test instance
     // to production, or a global stop syncing operation has wiped the store).
+    // TODO(lipalani) : Replace this function with the one below. This function
+    // stops the current sync cycle and purges the client. In the new model
+    // the former would be done by the |SyncProtocolError| and
+    // the latter(which is an action) would be done in ProfileSyncService
+    // along with the rest of the actions.
     virtual void OnShouldStopSyncingPermanently() = 0;
 
+    // Called for the syncer to respond to the error sent by the server.
+    virtual void OnSyncProtocolError(
+        const sessions::SyncSessionSnapshot& snapshot) = 0;
+
    protected:
     virtual ~Delegate() {}
   };