options: make default page list focusability match disable state

BUG=104000
TEST=see bug


Review URL: http://codereview.chromium.org/8873002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@113541 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/resources/options/browser_options.js

@@ -273,6 +273,7 @@ cr.define('options', function() {
       var disable = !this.shouldEnableCustomStartupPageControls();
       var startupPagesList = $('startupPagesList');
       startupPagesList.disabled = disable;
+      startupPagesList.setAttribute('tabindex', disable ? -1 : 0);
       // Explicitly set disabled state for input text elements.
       var inputs = startupPagesList.querySelectorAll("input[type='text']");
       for (var i = 0; i < inputs.length; i++)