Print preview: Display a dummy page when a user visits chrome://print directly.

chrome/browser/resources/print_preview/print_preview.css

 /* 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.
  */
 
 html {
   height: 100%;
 }
 
 body {
@@ skipping 402 matching lines @@
   display: -webkit-box;
 }
 
 html:not([toolkit=views]) .button-strip {
   -webkit-box-direction: reverse;
 }
 
 .button-strip button {
   display: block;
 }
+
+#dummy-box {
+  -webkit-box-align: stretch;
+  -webkit-box-flex: 1;
+  -webkit-box-orient: vertical;
+  background: #ccc;
+  display: -webkit-box;
+  height: 100%;
+  margin: 0;
+  min-height: 100%;
+  min-width: 100%;
+  position: absolute;
+  width: 100%;
+}
+
+#dummy-page {
+  -webkit-box-flex: 1;
+  background: white;
+  box-shadow: 0 0 8px rgba(0, 0, 0, .4);
+  height: auto;
+  margin: 10px;
+}
+
+#dummy-article {
+  line-height: 1.5;
+  margin-top: -10px;
+  position: absolute;
+  text-align: center;
+  top: 50%;
+  width: 100%;
+}
+
+#intentionally-blank {
+  color: black;
+  display: inline-block;
+  font-style: italic;
+  text-align: center;
+  text-decoration: none;
+  padding: 0 10px;
+}