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

chrome/browser/resources/print_preview/print_header.js

Index: chrome/browser/resources/print_preview/print_header.js
===================================================================
--- chrome/browser/resources/print_preview/print_header.js	(revision 104750)
+++ chrome/browser/resources/print_preview/print_header.js	(working copy)
@@ -38,13 +38,16 @@
      */
     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));
     },
 
     /**
@@ -58,10 +61,20 @@
         this.cancelButton_.classList.add('loading');
         this.summary_.innerHTML = localStrings.getString('printing');
       }
+      this.disableCancelButton_();
       requestToPrintDocument();
     },
 
     /**
+     * Disables the cancel button and removes its keydown event listener.
+     * @private
+     */
+    disableCancelButton_: function() {
+      window.onkeydown = null;
+      this.cancelButton_.disabled = true;
+    },
+
+    /**
      * 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.