listboxdefaulteventhandler in htmlselectelement is not called when mouse is released outside if listbox is non scrollable.
Hence onchange event is not fired for htmlselectelement. 
But when listbox is scrollable, Autoscrollcontroller is used to generate on change event.
Forcing Autoscrollcontroller to be used even when listbox is not scrollable. 
By commenting defaulthandled for mousemove in listboxdefaulteventhandler will cause handlemousedraggedevent to be called. 
This will start the Autoscrollcontroller for listbox selection. 
Which inturn will generate the onchange event.
The changes didnot cause any side effect and layout test failure.

BUG=317809, 94986

Review URL: https://codereview.chromium.org/120373005

git-svn-id: svn://svn.chromium.org/blink/trunk@164563 bbb929c8-8fbe-4397-9dbb-9b2b20218538