Do not change the value of a disabled SELECT element.

parseAttributes closes popup when the element becomes disabled.
    
We need to add some isDisabledFormControl checks to
menuListDefaultEventHandler because user events can be delivered to
disabled elements.

R=tkent
BUG=241079
TEST=automated

Review URL: https://codereview.chromium.org/159743002

git-svn-id: svn://svn.chromium.org/blink/trunk@167563 bbb929c8-8fbe-4397-9dbb-9b2b20218538