Integrate MDN content into API documentation.

utils/dartdoc/static/styles.css

 /* Reset */
 body, h1, h2, h3, h4, li, ol, p, pre, section, ul {
   margin: 0;
   padding: 0;
 }
 
 body {
   font-family: Georgia, serif;
   background: #e8e8e8;
   color: #333;
@@ skipping 210 matching lines @@
 }
 
 .footer p {
   font: 400 13px/22px 'Open Sans', 'Lucida Sans Unicode', 'Lucida Grande',
       sans-serif;
 }
 
 .method .doc,
 .field .doc {
   padding-left: 44px;
+  /* Ensure there is some space between members with no documentation. */
+  min-height: 22px;
 }
 
 .param {
   font: 600 14px 'Open Sans', 'Lucida Sans Unicode', 'Lucida Grande',
       sans-serif;
 }
 
 .crossref {
   font: 600 15px 'Open Sans', 'Lucida Sans Unicode', 'Lucida Grande',
       sans-serif;
 }
 
 .doc h1 {
   font: 700 17px/22px 'Open Sans', 'Lucida Sans Unicode', 'Lucida Grande',
       sans-serif;
   color: #666;
 }
 
 .doc h2 {
   font: 600 16px/22px 'Open Sans', 'Lucida Sans Unicode',
       'Lucida Grande', sans-serif;
   color: #666;
 }
 
+/* Style external links in docs differently. */
+.doc a[href^="http:"]:after,
+.doc a[href^="https:"]:after {
+  content: url('external-link.png');
+}
+
 /* Highlight members on hover so you can see which docs are for which member. */
 .method:hover,
 .field:hover {
   margin: 0 -22px;
   border: solid 4px hsl(40, 100%, 85%);
   padding: 0 18px;
   border-top: none;
   border-bottom: none;
 }
 
@@ skipping 95 matching lines @@
 }
 
 p {
   border-left: solid 4px purple;
 }
 
 section {
   border-left: solid 4px gray;
 }
 */