Test that setting scrollLeft on an overflow:hidden element works with both scroll behaviors

This is a testharness.js-based test.
PASS Scroll x:1, y:0, smooth:false 
PASS Scroll x:4, y:0, smooth:false 
PASS Scroll x:20, y:0, smooth:true 
PASS Scroll x:40, y:0, smooth:true 
PASS Scroll x:4000, y:0, smooth:true 
PASS Scroll x:10, y:0, smooth:true 
Harness: the test ran to completion.