Re-land "Improve support for :read-only and :read-write pseudoclasses".

LayoutTests/fast/forms/resources/select-live-pseudo-selectors.js

 description("This test performs a check that :valid/:invalid CSS psudo selectors are lively applied.");
 
 // Setup for static elements.
 var form = document.createElement('form');
 document.body.appendChild(form);
 var nonForm = document.createElement('div');
 document.body.appendChild(nonForm);
 
 function mouseDownOnSelect(selId, index, modifier) {
     var sl = document.getElementById(selId);
@@ skipping 42 matching lines @@
 function backgroundOf(el) {
     if (typeof(el) == 'string')
         el = document.getElementById(el);
     return document.defaultView.getComputedStyle(el, null).getPropertyValue('background-color');
 }
 
 var elBackground = 'backgroundOf(el)';
 var invalidColor = 'rgb(255, 0, 0)';
 var normalColor = 'rgb(255, 255, 255)';
 var disabledColor = 'rgb(0, 0, 0)';
-var readOnlyColor = 'rgb(0, 255, 0)'
 var transparentColor = 'rgba(0, 0, 0, 0)';
 var validColor = 'rgb(0, 0, 255)';
 
 // --------------------------------
 //     willValidate change
 // --------------------------------
 var el = makeInvalid();
 var o1 = appendOption('', el);
 var o2 = appendOption('X', el);
 o1.selected = true;
@@ skipping 132 matching lines @@
 // --------------------------------
 debug('Change required:');
 el = makeInvalid();
 o1 = appendOption('', el);
 o2 = appendOption('X', el);
 o1.selected = true;
 el.required = false;
 shouldBe(elBackground, 'validColor');
 el.required = true;
 shouldBe(elBackground, 'invalidColor');