Enable a11y audit for chrome://print and fix failing tests.

chrome/browser/resources/print_preview/previewarea/margin_control.js

Index: chrome/browser/resources/print_preview/previewarea/margin_control.js
diff --git a/chrome/browser/resources/print_preview/previewarea/margin_control.js b/chrome/browser/resources/print_preview/previewarea/margin_control.js
index 7ec2527e7a17e02389387adba3c9c806b7ec8b3d..63f67aeb62639bba7706b935cf88450ff823f9ee 100644
--- a/chrome/browser/resources/print_preview/previewarea/margin_control.js
+++ b/chrome/browser/resources/print_preview/previewarea/margin_control.js
@@ -187,6 +187,7 @@ cr.define('print_preview', function() {
     /** @param {boolean} isVisible Whether the margin control is visible. */
     setIsVisible: function(isVisible) {
       this.getElement().classList.toggle('invisible', !isVisible);
+      this.getElement().setAttribute('aria-hidden', !isVisible);
     },
 
     /** @return {boolean} Whether the margin control is in an error state. */
@@ -324,10 +325,6 @@ cr.define('print_preview', function() {
       this.tracker.add(
           this.getElement(), 'mousedown', this.onMouseDown_.bind(this));
       this.tracker.add(
-          this.getElement(),
-          'webkitTransitionEnd',
-          this.onWebkitTransitionEnd_.bind(this));
-      this.tracker.add(
           this.textbox_, 'input', this.onTextboxInput_.bind(this));
       this.tracker.add(
           this.textbox_, 'keydown', this.onTextboxKeyDown_.bind(this));
@@ -371,18 +368,6 @@ cr.define('print_preview', function() {
     },
 
     /**
-     * Called when opacity CSS transition ends.
-     * @private
-     */
-    onWebkitTransitionEnd_: function(event) {

[Dan Beam, 2014/10/15 21:37:31]

not lgtm, add back before you land
https://code.google.com/p/chromium/codesearch#chromium/src/chrome/browser/res...

[hcarmona, 2014/10/17 01:35:53]

Acknowledged.

-      if (event.propertyName != 'opacity')
-        return;
-      var elStyle = window.getComputedStyle(this.getElement());
-      var opacity = parseInt(elStyle.getPropertyValue('opacity'), 10);
-      this.textbox_.setAttribute('aria-hidden', opacity == 0);
-    },
-
-    /**
      * Called when textbox content changes. Starts text change timeout.
      * @private
      */