ChromeOS OOBE: display icons specific to screen DPI.

chrome/browser/resources/chromeos/login/oobe_welcome_secondary_button.css

 /* Copyright 2016 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. */
 :host {
   color: #5a5a5a;
   height: 32px; /* = 28 + 2 * 2px keyboad-focus border */
   max-width: 300px;
   min-width: 120px;
 }
 
@@ skipping 33 matching lines @@
   font-size: 12px;
   text-transform: none;
 }
 
 iron-icon {
   --iron-icon-height: 16px;
   --iron-icon-width: 16px;
   color: #5a5a5a;
   margin: 0 8px 0 0;
 }
+
+@media all and (-webkit-max-device-pixel-ratio: 1.5) {
+  #icon2x {
+    display: none;
+  }
+}
+
+@media all and (-webkit-min-device-pixel-ratio: 1.5) {
+  #icon1x {
+    display: none;
+  }
+}