IndexedDB: Rely on bindings for enum validation

LayoutTests/storage/indexeddb/exceptions-expected.txt

 Test that expected exceptions are thrown per IndexedDB spec.
 
 On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
 
 
 indexedDB = self.indexedDB || self.webkitIndexedDB || self.mozIndexedDB || self.msIndexedDB || self.OIndexedDB;
 
 dbname = "exceptions.html"
 indexedDB.deleteDatabase(dbname)
 indexedDB.open(dbname)
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 Exception message: Failed to execute 'openCursor' on 'IDBObjectStore': The parameter is not a valid key.
 The transaction this IDBObjectStore belongs to is not active.
 Expecting exception from storeFromInactiveTransaction.openCursor()
 PASS Exception was thrown.
 PASS code is 0
 PASS ename is 'TransactionInactiveError'
 Exception message: Failed to execute 'openCursor' on 'IDBObjectStore': The transaction has finished.
 The value for the direction parameter is invalid.
 Expecting TypeError exception from store.openCursor(0, 'invalid-direction')
 PASS Exception was thrown.
-PASS store.openCursor(0, 'invalid-direction') threw TypeError: Failed to execute 'openCursor' on 'IDBObjectStore': The direction provided ('invalid-direction') is not one of 'next', 'nextunique', 'prev', or 'prevunique'.
+PASS store.openCursor(0, 'invalid-direction') threw TypeError: Failed to execute 'openCursor' on 'IDBObjectStore': The provided value 'invalid-direction' is not a valid enum value of type IDBCursorDirection.
 
 IDBObjectStore.openKeyCursor()
 If the range parameter is specified but is not a valid key or a key range, this method throws a DOMException of type DataError.
 Expecting exception from store.openKeyCursor({})
 PASS Exception was thrown.
 PASS code is 0
 PASS ename is 'DataError'
 Exception message: Failed to execute 'openKeyCursor' on 'IDBObjectStore': The parameter is not a valid key.
 The transaction this IDBObjectStore belongs to is not active.
 Expecting exception from storeFromInactiveTransaction.openKeyCursor()
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 If the requested object store is not in this transaction's scope.
 Expecting exception from db.transaction('store').objectStore('otherStore')
 PASS Exception was thrown.
 PASS code is DOMException.NOT_FOUND_ERR
 PASS ename is 'NotFoundError'
 Exception message: Failed to execute 'objectStore' on 'IDBTransaction': The specified object store was not found.
 PASS successfullyParsed is true
 
 TEST COMPLETE