Reset only invalid custom margins.

chrome/test/data/webui/print_preview.js

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * Test fixture for print preview WebUI testing.
  * @constructor
  * @extends {testing.Test}
  */
 function PrintPreviewWebUITest() {
@@ skipping 704 matching lines @@
     'disableColorOption': false,
     'setColorAsDefault': true,
     'disableCopiesOption': true,
     'disableLandscapeOption': true,
     'printerDefaultDuplexValue': 0
   };
   this.nativeLayer_.dispatchEvent(capsSetEvent);
 
   var previewGenerator = mock(print_preview.PreviewGenerator);
   printPreview.previewArea_.previewGenerator_ = previewGenerator.proxy();
-  previewGenerator.expects(exactly(6)).requestPreview();
+  previewGenerator.expects(atLeastOnce()).requestPreview();
 
   var barDestination;
   var destinations = printPreview.destinationStore_.destinations;
   for (var destination, i = 0; destination = destinations[i]; i++) {
     if (destination.id == 'BarDevice') {
       barDestination = destination;
       break;
     }
   }
 
@@ skipping 25 matching lines @@
   expectEquals(true, previewFailedMessageEl.hidden);
 
   var printFailedMessageEl =
       previewAreaEl.getElementsByClassName('preview-area-print-failed')[0];
   expectEquals(true, printFailedMessageEl.hidden);
 
   var customMessageEl =
       previewAreaEl.getElementsByClassName('preview-area-custom-message')[0];
   expectEquals(false, customMessageEl.hidden);
 });