Remove 'Enable' button on unsupported platforms. Added 'No hosts' message.

remoting/webapp/main.css

 /* Copyright (c) 2012 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, body, div, span, applet, object, iframe, h1, h2, h3, h4, h5, h6, p,
 blockquote, pre, a, abbr, acronym, address, big, cite, code, del, dfn, em,
 font, img, ins, kbd, q, s, samp, small, strike, strong, sub, sup, tt, var, dl,
 dt, dd, ol, ul, li, fieldset, form, label, legend, table, caption, tbody,
 tfoot, thead, tr, th, td, button {
@@ skipping 225 matching lines @@
   line-height: 24px;
   display: inline-block;
   margin-__MSG_@@bidi_start_edge__: 10px;
 }
 
 h2 {
   font-size: 16px;
   line-height:24px;
   font-weight: normal;
   color: #222;
+  margin-bottom: 10px;
 }
 
 section > h2 {
   color: #666;
 }
 
 header {
   display: -webkit-box;
   width: 100%;
 }
@@ skipping 34 matching lines @@
 }
 
 .clickable {
   cursor: pointer;
 }
 
 .box {
   display: -webkit-box;
 }
 
+.host-list-empty-instructions {
+  padding-__MSG_@@bidi_start_edge__: 36px;
+  color: #666;
+  background-image: url('host_setup_instructions.png');
+  background-repeat: no-repeat;
+  background-position: -3px -2px;
+}
+
+#host-list-empty-hosting-supported {
+  margin-top: 14px;
+  padding-top: 20px;
+  border-top: 1px solid #E5E5E5;
+  background-position-y: 18px;
+}
+
 .selectable {
   -webkit-user-select: text;
   cursor: text;
 }
 
 .section-row {
   display: -webkit-box;
   -webkit-box-align: center;
   padding: 10px 0;
   border-top: 1px solid #EBEBEB;
@@ skipping 54 matching lines @@
 }
 
 .mode-select-button-column {
   text-align: __MSG_@@bidi_end_edge__;
 }
 
 .mode-select-button-column button {
   min-width: 72px;
 }
 
-.host-list-table {
-  width: 100%;
-  border-spacing: 0;
-}
-
 td {
   vertical-align: middle;
 }
 
 .host-online.clickable:hover,
 .host-online.clickable.child-focused {
   background-color: #f2f2f2;
 }
 
 .host-list-rename-icon,
@@ skipping 165 matching lines @@
 #set-pin-table td {
   border-bottom: 6px solid transparent;
   text-align: right;
 }
 
 #top-secondary {
   margin-top: 10px
 }
 
 #webapp-description {
-  margin: 10px 0;
+  margin-bottom: 10px;
 }
 
 #why-is-this-safe {
   display: inline-block;
   margin-top: 7px;
 }
 
 * {
   box-sizing: border-box;
 }
 
 /*
  * Setting hidden on elements that match some rule overriding 'display' doesn't
  * do what you would expect unless this is made explicit (and !important).
  */
 [hidden] {
   display: none !important;
 }