Display a pause screen in a paused browser.

lib/src/runner/browser/static/host.css

 /* Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
  * for details. All rights reserved. Use of this source code is governed by a
  * BSD-style license that can be found in the LICENSE file. */
 
 iframe {
   /* We would use display: none here, but then Firefox fails to properly compute
    * styles. See #274 */
   visibility: hidden;
 }
 
+#play {
+  display: none;
+  cursor: pointer;
+}
+
+#dark {
+  display: none;
+}
+
+.paused #play {
+  display: block;
+}
+
+.paused #dark {
+  display: block;
+  position: absolute;
+  width: 100%;
+  height: 100%;
+  top: 0;
+  right: 0;
+  background-color: rgba(0, 0, 0, 0.5);
+}
+
+.paused #right-flank, .paused #right-ear, .paused #right-paw,
+.paused #left-flank,  .paused #left-ear,  .paused #left-paw {
+  -webkit-animation-play-state: paused;
+          animation-play-state: paused;
+}
+
 /* Compiled output from
  * http://codepen.io/mknadler/pen/11b75cb014a3c382f54abf527655af21. */
 
 svg {
   position: absolute;
   margin: auto;
   left: 0;
   right: 0;
   bottom: 0;
   top: 0;
@@ skipping 239 matching lines @@
     -webkit-transform: translate(110px, 0px) scale(0.4);
             transform: translate(110px, 0px) scale(0.4);
     fill: #00A6E4;
   }
   80% {
     -webkit-transform: translate(0px, 0px) scale(1);
             transform: translate(0px, 0px) scale(1);
     fill: #0074C1;
   }
 }