Let buttons and select controls in Print Preview to handle Enter key.

chrome/browser/resources/print_preview/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.
 
 // TODO(rltoscano): Move data/* into print_preview.data namespace
 
 var localStrings = new LocalStrings(templateData);
 
 <include src="component.js"/>
 
@@ skipping 751 matching lines @@
           this.openSystemPrintDialog_();
           e.preventDefault();
           return;
         }
       }
 
       if (e.keyCode == 13 /*enter*/ &&
           !this.destinationSearch_.getIsVisible() &&
           this.printTicketStore_.isTicketValid()) {
         assert(this.uiState_ == PrintPreview.UiState_.READY,
-          'Trying to print when not in ready state: ' + this.uiState_);
-        this.printDocumentOrOpenPdfPreview_(false /*isPdfPreview*/);
-        e.preventDefault();
+            'Trying to print when not in ready state: ' + this.uiState_);
+        var activeElementTag = document.activeElement ?
+            document.activeElement.tagName.toUpperCase() : '';
+        if (activeElementTag != 'BUTTON' && activeElementTag != 'SELECT') {
+          this.printDocumentOrOpenPdfPreview_(false /*isPdfPreview*/);
+          e.preventDefault();
+        }
         return;
       }
 
       // Pass certain directional keyboard events to the PDF viewer.
       this.previewArea_.handleDirectionalKeyEvent(e);
     },
 
     /**
      * Called when native layer receives invalid settings for a print request.
      * @private
@@ skipping 207 matching lines @@
 <include src="search/recent_destination_list.js"/>
 <include src="search/destination_list_item.js"/>
 <include src="search/destination_search.js"/>
 <include src="search/search_box.js"/>
 <include src="search/fedex_tos.js"/>
 
 window.addEventListener('DOMContentLoaded', function() {
   printPreview = new print_preview.PrintPreview();
   printPreview.initialize();
 });