Add survey js to docs web site (#13210)

* Fixed typo in navigator.dart doc comments

* Added survey js to docs template

dev/docs/survey.html

+<script async="" defer="" 
+  src="//www.google.com/insights/consumersurveys/async_survey?site=i2bdmo2dzky7fqws25nicgx5f4">
+</script>
\ No newline at end of file

dev/tools/dartdoc.dart

@@ -95,6 +95,7 @@ dependencies:
     'global', 'run', 'dartdoc',
     '--header', 'styles.html',
     '--header', 'analytics.html',
+    '--header', 'survey.html',
     '--footer-text', 'lib/footer.html',
     '--exclude', 'temp_doc',
     '--favicon=favicon.ico',