[Search] Add a header image to the promo flow.

chrome/browser/resources/contextual_search/promo.css

 /* Copyright 2014 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.
 */
 @font-face {
   font-family: 'Roboto2';
   font-weight: 400;
   src: local('Roboto'), local('Roboto2-Regular'),
       url(/roboto.woff2) format('woff2'), url(/roboto.woff) format('woff');
 }
@@ skipping 33 matching lines @@
 #container.hide {
   -webkit-transform: scale(0.95);
   -webkit-transition-duration: 218ms;
   -webkit-transition-property: opacity, -webkit-transform;
   opacity: 0;
 }
 
 #description {
   font-size: 16px;
   line-height: 1.4em;
-  margin: 32px 16px 4px 16px;
+  margin: 24px 16px 4px 16px;
 }
 
 #heading {
   font-size: 24px;
   letter-spacing: 1px;
   margin-top: 0;
   text-align: center;
 }
+
+#header-image {
+  display: block;
+  height: 100px;
+  margin: 0 auto 24px auto;
+}