Make default argument to Iterable.join be "".

sdk/lib/web_sql/dart2js/web_sql_dart2js.dart

 /**
  * An API for storing data in the browser that can be queried with SQL.
  *
  * **Caution:** this specification is no longer actively maintained by the Web
  * Applications Working Group and may be removed at any time.
  * See [the W3C Web SQL Database specification](http://www.w3.org/TR/webdatabase/)
  * for more information.
  *
  * The [dart:indexed_db] APIs is a recommended alternatives.
  */
@@ skipping 217 matching lines @@
   }
 
   dynamic fold(dynamic initialValue, dynamic combine(dynamic, Map)) {
     return IterableMixinWorkaround.fold(this, initialValue, combine);
   }
 
   bool contains(Map element) => IterableMixinWorkaround.contains(this, element);
 
   void forEach(void f(Map element)) => IterableMixinWorkaround.forEach(this, f);
 
-  String join([String separator]) =>
+  String join([String separator = ""]) =>
       IterableMixinWorkaround.joinList(this, separator);
 
   Iterable map(f(Map element)) =>
       IterableMixinWorkaround.mapList(this, f);
 
   Iterable<Map> where(bool f(Map element)) =>
       IterableMixinWorkaround.where(this, f);
 
   Iterable expand(Iterable f(Map element)) =>
       IterableMixinWorkaround.expand(this, f);
@@ skipping 203 matching lines @@
 // BSD-style license that can be found in the LICENSE file.
 
 
 @DocsEditable
 @DomName('SQLTransactionSync')
 @SupportedBrowser(SupportedBrowser.CHROME)
 @SupportedBrowser(SupportedBrowser.SAFARI)
 @Experimental
 abstract class _SQLTransactionSync native "*SQLTransactionSync" {
 }