[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 bd7d01dc0976eee6222415e8db7cc196597f9601..00e5f338a2b178587ba3baa5d1d5c4497e7b9ad3 100644
--- a/components/history/core/browser/history_backend.cc
+++ b/components/history/core/browser/history_backend.cc
@@ -1042,6 +1042,12 @@ 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) {