Switch IDB Database.transaction to use a template to do the right type conversions

sdk/lib/indexed_db/dart2js/indexed_db_dart2js.dart

 /**
  * A client-side key-value store with support for indexes.
  *
  * Many browsers support IndexedDB—a web standard for
  * an indexed database.
  * By storing data on the client in an IndexedDB,
  * a web app gets some advantages, such as faster performance and persistence.
  * To find out which browsers support IndexedDB,
  * refer to [Can I Use?](http://caniuse.com/#feat=indexeddb)
  *
@@ skipping 362 matching lines @@
     return _transaction(storeName, mode);
   }
 
   Transaction transactionList(List<String> storeNames, String mode) {
     if (mode != 'readonly' && mode != 'readwrite') {
       throw new ArgumentError(mode);
     }
     List storeNames_1 = convertDartToNative_StringArray(storeNames);
     return _transaction(storeNames_1, mode);
   }
-  
+
   Transaction transactionStores(DomStringList storeNames, String mode) {
     if (mode != 'readonly' && mode != 'readwrite') {
       throw new ArgumentError(mode);
     }
     return _transaction(storeNames, mode);
   }
 
   @JSName('transaction')
   Transaction _transaction(stores, mode) native;
 
@@ skipping 1052 matching lines @@
   @Creates('int|String|Null')
   @Returns('int|String|Null')
   final int newVersion;
 
   @DomName('IDBVersionChangeEvent.oldVersion')
   @DocsEditable()
   @Creates('int|String|Null')
   @Returns('int|String|Null')
   final int oldVersion;
 }