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

chrome/browser/resources/print_preview/print_preview.js

Index: chrome/browser/resources/print_preview/print_preview.js
diff --git a/chrome/browser/resources/print_preview/print_preview.js b/chrome/browser/resources/print_preview/print_preview.js
index 9aca1011579918c2ddbf3815ab47b5497073101c..8c1d3829d9acfc1df8870a15168f764b9ef2b283 100644
--- a/chrome/browser/resources/print_preview/print_preview.js
+++ b/chrome/browser/resources/print_preview/print_preview.js
@@ -769,9 +769,13 @@ cr.define('print_preview', function() {
           !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;
       }