Creates an IDBDatabase wrapper object. The database object has methods for
setting the version to change the structure of the database and for creating
transactions to get or modify the stored records. Should not be created
directly, call goog.db.openDatabase to set up the connection.
Event representing a (possibly attempted) change in the database structure.
At time of writing, no Chrome versions support oldVersion or newVersion. See
http://crbug.com/153122.