Don't persist and sync omnibox extension keywords.

components/search_engines/keyword_table.cc

Index: components/search_engines/keyword_table.cc
diff --git a/components/search_engines/keyword_table.cc b/components/search_engines/keyword_table.cc
index 447ebfbeba81bbad79392c66f990772d6e7800f4..08dea926567ef34ed5ee773bd6cd5d182d854ed1 100644
--- a/components/search_engines/keyword_table.cc
+++ b/components/search_engines/keyword_table.cc
@@ -235,6 +235,9 @@ bool KeywordTable::MigrateToVersion(int version,
     case 53:
       *update_compatible_version = true;
       return MigrateToVersion53AddNewTabURLColumn();
+    case 59:
+      *update_compatible_version = true;
+      return MigrateToVersion59RemoveExtensionKeywords();
   }
 
   return true;
@@ -451,6 +454,11 @@ bool KeywordTable::MigrateToVersion53AddNewTabURLColumn() {
                       "VARCHAR DEFAULT ''");
 }
 
+bool KeywordTable::MigrateToVersion59RemoveExtensionKeywords() {
+  return db_->Execute("DELETE FROM keywords "
+                      "WHERE url LIKE 'chrome-extension://%'");
+}
+
 // static
 bool KeywordTable::GetKeywordDataFromStatement(const sql::Statement& s,
                                                TemplateURLData* data) {