Currently, setting new scale to tiled backing store does not apply to its viewport. So, it makes tiled backing store have a wrong viewport after the setting.
Created attachment 56147 [details] patch
Comment on attachment 56147 [details] patch r- for the lack of tests. I guess you can't test this using the DRT framework, if not, add a manual test to WebCore/manual-tests/.
*** This bug has been marked as a duplicate of bug 39218 ***