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

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

Index: chrome/browser/resources/print_preview/previewarea/preview_area.js
diff --git a/chrome/browser/resources/print_preview/previewarea/preview_area.js b/chrome/browser/resources/print_preview/previewarea/preview_area.js
index 85578a383dfe8fa344883b867d75d60cc899a112..bf921a544dcce7811f9c708a8d1bfe3302262cfd 100644
--- a/chrome/browser/resources/print_preview/previewarea/preview_area.js
+++ b/chrome/browser/resources/print_preview/previewarea/preview_area.js
@@ -199,7 +199,10 @@ cr.define('print_preview', function() {
     OPEN_SYSTEM_DIALOG_BUTTON: 'preview-area-open-system-dialog-button',
     OPEN_SYSTEM_DIALOG_BUTTON_THROBBER:
         'preview-area-open-system-dialog-button-throbber',
-    OVERLAY: 'preview-area-overlay-layer'
+    OVERLAY: 'preview-area-overlay-layer',
+    OVERLAYED: 'preview-area-overlayed',
+    MARGIN_CONTROL: 'margin-control',
+    PREVIEW_AREA: 'preview-area-plugin-wrapper'
   };
 
   /**
@@ -504,8 +507,27 @@ cr.define('print_preview', function() {
             PreviewArea.MessageIdClassMap_[messageId])[0];
       setIsVisible(messageEl, true);
 
-      // Show overlay.
+      this.showOverlay_();
+    },
+
+    /**
+     * Shows the message overlay.
+     * @private
+     */
+    showOverlay_: function() {
       this.overlayEl_.classList.remove(PreviewArea.Classes_.INVISIBLE);
+
+      // Hide all controls that will be hidden when the overlay is visible.
+      var marginControls = this.getElement().getElementsByClassName(
+          PreviewArea.Classes_.MARGIN_CONTROL);
+      for (var i = 0; i < marginControls.length; ++i) {
+        marginControls[i].classList.add(PreviewArea.Classes_.OVERLAYED);
+      }
+      var previewAreaControls = this.getElement().getElementsByClassName(
+          PreviewArea.Classes_.PREVIEW_AREA);
+      for (var i = 0; i < previewAreaControls.length; ++i) {
+        previewAreaControls[i].classList.add(PreviewArea.Classes_.OVERLAYED);
+      }
     },
 
     /**
@@ -514,6 +536,20 @@ cr.define('print_preview', function() {
      */
     hideOverlay_: function() {
       this.overlayEl_.classList.add(PreviewArea.Classes_.INVISIBLE);
+
+      // Display all controls that will be visible when the overlay is no longer
+      // visible.
+      var marginControls = this.getElement().getElementsByClassName(
+          PreviewArea.Classes_.MARGIN_CONTROL);
+      for (var i = 0; i < marginControls.length; ++i) {
+        marginControls[i].classList.remove(PreviewArea.Classes_.OVERLAYED);
+      }
+      var previewAreaControls = this.getElement().getElementsByClassName(
+          PreviewArea.Classes_.PREVIEW_AREA);
+      for (var i = 0; i < previewAreaControls.length; ++i) {
+        previewAreaControls[i].classList.remove(PreviewArea.Classes_.OVERLAYED);
+      }
+
       // Disable jumping animation to conserve cycles.
       var jumpingDotsEl = this.getElement().querySelector(
           '.preview-area-loading-message-jumping-dots');