update NDK doxygen templates to create DevSite-style HTML.

Previously, we had doxygen create .jd files with some syntax that
was parsed by the DocLava build tools when creating the final HTML
files for the website. But now that we're publishing these docs through
Piper, we don't need to run them through DocLava anymore. So with this
change, we now create .html files that then need to be copied to
google3/googledata/devsite/site-android/en/ndk/
where they can be immediately published via devsite once merged.
bug: 29943712

Change-Id: I8af5555f802e8c0122378bd504ad4308ff9aad56
diff --git a/docs/header.html b/docs/header.html
new file mode 100644
index 0000000..04727b3
--- /dev/null
+++ b/docs/header.html
@@ -0,0 +1,10 @@
+<html devsite>
+<head>
+  <meta name="top_category" value="ndk" />
+  <meta name="subcategory" value="reference" />
+  <meta name="book_path" value="/ndk/reference/_book.yaml" />
+  <title>$title</title>
+  <link rel="stylesheet" type="text/css" href="doxygen-dac.css">
+</head>
+<body>
+<div id="top"><!-- we must have this tag, it's closed by doxygen. ¯\_(ツ)_/¯ -->