ChromeOS OOBE: Add new image to Welcome dialog.

chrome/browser/resources/chromeos/login/oobe_welcome_dialog.html

 <!-- 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. -->
 
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/classes/iron-flex-layout.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-styles/color.html">
 
 <!--
   OOBE Welcome screen
 -->
 <dom-module name="oobe-welcome-dialog">
   <template>
     <link rel="stylesheet" href="oobe_dialog_host.css">
     <link rel="stylesheet" href="oobe_welcome_dialog.css">
     <div class="layout horizontal flex">
       <div class="vertical-margin"></div>
       <div class="welcome-content flex layout vertical center">
         <h1 id="title" i18n-content="networkScreenGreeting"></h1>
-        <!-- TODO(alemate): Display images depending on screen ppi. -->
-        <img id="welcomeIllustration" src="images/welcome_illustration_2x.png">
+        <img id="welcomeIllustration"
+            srcset="images/welcome_illustration_1x.png 1x,
+                    images/welcome_illustration_2x.png 2x">
         <div hidden="[[!debuggingLinkVisible]]">
           <a href="#" i18n-content="debuggingFeaturesLink"
               on-tap="onDebuggingLinkClicked_"></a>
         </div>
         <div class="flex"></div>
         <div id="buttons" class="layout horizontal center">
           <oobe-welcome-secondary-button id="languageSelectionButton"
               icon="icons:language" on-tap="onLanguageClicked_"
               aria-label="[[formatMessage_('languageButtonLabel',
                   currentLanguage)]]">
@@ skipping 13 matching lines @@
               inverse on-tap="onNextClicked_">
             <div i18n-content="welcomeNextButtonText"></div>
           </oobe-text-button>
         </div>
         <div id="bottom-margin"></div>
       </div>
       <div class="vertical-margin"></div>
     </div>
   </template>
 </dom-module>