Print Preview: Keep the cancel button enabled whenever possible. Hook up the escape key to cancel.

chrome/browser/resources/print_preview/print_header.js

 // Copyright (c) 2011 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.
 
 cr.define('print_preview', function() {
   'use strict';
 
   /**
    * Creates a PrintHeader object. This object encapsulates all the elements
    * and logic related to the top part of the left pane in print_preview.html.
@@ skipping 20 matching lines @@
     get summary() {
       return this.summary_;
     },
 
     /**
      * Adding event listeners where necessary. Listeners take care of changing
      * their behavior depending on the current state, no need to remove them.
      */
     addEventListeners: function() {
       this.cancelButton_.onclick = function() {
-        chrome.send('closePrintPreviewTab');
-      };
+        this.disableCancelButton();
+        closePrintPreviewTab();
+      }.bind(this);
       this.printButton_.onclick = this.onPrintButtonClicked_.bind(this);
       document.addEventListener('updateSummary',
                                 this.updateSummary_.bind(this));
       document.addEventListener('updatePrintButton',
                                 this.updatePrintButton_.bind(this));
+      document.addEventListener('disableCancelButton',
+                                this.disableCancelButton.bind(this));
+    },
+
+    /**
+     * Disables the cancel button and removes its keydown event listener.
+     */
+    disableCancelButton: function() {
+      window.onkeydown = null;
+      this.cancelButton_.disabled = true;
     },
 
     /**
      * Listener executing whenever |this.printButton_| is clicked.
      * @private
      */
     onPrintButtonClicked_: function() {
       var printToPDF = getSelectedPrinterName() == PRINT_TO_PDF;
       if (!printToPDF) {
         this.printButton_.classList.add('loading');
         this.cancelButton_.classList.add('loading');
         this.summary_.innerHTML = localStrings.getString('printing');
       }
+      this.disableCancelButton();
       requestToPrintDocument();
     },
 
     /**
      * Updates the state of |this.printButton_| depending on the user selection.
      * The button is enabled only when the following conditions are true.
      * 1) The selected page ranges are valid.
      * 2) The number of copies is valid (if applicable).
      * @private
      */
@@ skipping 52 matching lines @@
       // Removing extra spaces from within the string.
       html = html.replace(/\s{2,}/g, ' ');
       this.summary_.innerHTML = html;
     },
   };
 
   return {
     PrintHeader: PrintHeader,
   };
 });