[USS] Implement ApplySyncChanges and OnURLVisited/Modified/Deleted.

components/history/core/browser/history_backend.cc

Index: components/history/core/browser/history_backend.cc
diff --git a/components/history/core/browser/history_backend.cc b/components/history/core/browser/history_backend.cc
index 1c4aa6a0436526c8c33c228708c1e585b47a3127..a28868c92141253a6483dd67509046576671820d 100644
--- a/components/history/core/browser/history_backend.cc
+++ b/components/history/core/browser/history_backend.cc
@@ -1039,6 +1039,12 @@ bool HistoryBackend::GetURL(const GURL& url, URLRow* url_row) {
   return false;
 }
 
+bool HistoryBackend::GetURLByID(URLID url_id, URLRow* url_row) {
+  if (db_)
+    return db_->GetURLRow(url_id, url_row);
+  return false;
+}
+
 void HistoryBackend::QueryURL(const GURL& url,
                               bool want_visits,
                               QueryURLResult* result) {