IndexedDB: Tests for unknown serialized data versions in backing stores.
If the serialized data format (SerializedScriptValue) is advanced, a data
store is created, then the user downgrades to an older browser version but
does not delete the profile directory we treat this the same as an unknown
schema version and blow away the backing store. This is not a supported
scenario but it happens frequently enough that we don't want to wedge such
users with silently corrupted data.
This is just a test. See http://webkit.org/b/102243
for the patch.