IndexedDB: Log exception messages

LayoutTests/storage/indexeddb/mozilla/bad-keypath-expected.txt

 Test IndexedDB adding property with invalid keypath
 
 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 = "bad-keypath.html"
 indexedDB.deleteDatabase(dbname)
 indexedDB.open(dbname)
 objectStore = db.createObjectStore('foo', { keyPath: 'keyPath' });
 request = objectStore.add({ keyPath: 'foo' });
 Expecting exception from request = objectStore.add({});
 PASS Exception was thrown.
 PASS code is 0
 PASS ename is 'DataError'
+Exception message: Evaluating the object store's key path did not yield a value.
 PASS successfullyParsed is true
 
 TEST COMPLETE