Generate reference nav to _book.yaml for devsite builds.

Change-Id: Iea0e1031b0d757664b8994096010dd92b98ca883

tools/droiddoc/templates-sdk-dev/yaml_navtree.cs

@@ -0,0 +1,14 @@
+<?cs
+
+# print out the yaml nav for the reference docs, only printing the title,
+path, and status_text (API level) for each package.
+
+?>
+reference:<?cs
+each:page = docs.pages?><?cs
+  if:page.type == "package"?>
+- title: <?cs var:page.label ?>
+  path: <?cs var:page.link ?>
+  status_text: apilevel-<?cs var:page.apilevel ?><?cs
+  /if?><?cs
+/each ?>