[indexeddb] Using IDBDatabaseSync.close or IDBFactorySync.deleteDatabase inside transaction's callback method

[Israel Hilerio]

What do you think about NOT allowing IDBFactorySync.deleteDatabase and 
IDBDatabaseSync.close to be called from within the transaction callback method 
of IDBDatabaseSync.transaction or IDBDatabaseSync.setVersion?  This will reduce 
the number of possible deadlocks inside the transaction callback.

We can throw an IDBDatabaseException with NOT_ALLOWED_ERR if a developer tries 
to do this.

Israel