[Sync] Try to fix race conditions in CookieJarMismatch.

components/sync/driver/glue/sync_backend_host_impl.h

Index: components/sync/driver/glue/sync_backend_host_impl.h
diff --git a/components/sync/driver/glue/sync_backend_host_impl.h b/components/sync/driver/glue/sync_backend_host_impl.h
index 00aebd3bb1b5a8d6213b6edc488c2c8437874464..5c27a10eab23b26016b7f63c0507200a0b52a076 100644
--- a/components/sync/driver/glue/sync_backend_host_impl.h
+++ b/components/sync/driver/glue/sync_backend_host_impl.h
@@ -91,7 +91,9 @@ class SyncBackendHostImpl : public SyncEngine, public InvalidationHandler {
   void RefreshTypesForTest(ModelTypeSet types) override;
   void ClearServerData(
       const SyncManager::ClearServerDataCallback& callback) override;
-  void OnCookieJarChanged(bool account_mismatch, bool empty_jar) override;
+  void OnCookieJarChanged(bool account_mismatch,
+                          bool empty_jar,
+                          const base::Closure& callback) override;
 
   // InvalidationHandler implementation.
   void OnInvalidatorStateChange(InvalidatorState state) override;
@@ -193,6 +195,8 @@ class SyncBackendHostImpl : public SyncEngine, public InvalidationHandler {
   void ClearServerDataDoneOnFrontendLoop(
       const SyncManager::ClearServerDataCallback& frontend_callback);
 
+  void OnCookieJarChangedDoneOnFrontendLoop(const base::Closure& callback);
+
   SyncClient* const sync_client_;
 
   // The task runner where all the sync engine operations happen.