Scrollbars without extent get extent when maximum is reduced

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Run test below
2. Observe that it fails
3. File issue on code.google.com

What is the expected output? What do you see instead?

Expected output: scrollbars that don't have an extent thumb should never have 
extent. But it seems that they acquire it when the maximum value is reduced.

What version of the product are you using? On what operating system?

svn rev 1917, Chromium Version 20.0.1132.47 Ubuntu 12.04 (144678)

Please provide any additional information below.

function testScrollBarBehaviour()
{
    var scroll = new goog.ui.Slider;
    scroll.setMaximum(10000);
    scroll.setValue(9998);
    assertEquals(0, scroll.getExtent());
    scroll.setMaximum(10);
    scroll.setValue(8);
    assertEquals(8, scroll.getValue());
    assertEquals(0, scroll.getExtent());
}

Note: this is not only an issue with invisible (unrendered) scroll bars. It 
happens with rendered ones too. But rendering is not necessary to reproduce the 
issue.

Original issue reported on code.google.com by ch...@aptivate.org on 12 Dec 2012 at 3:34