Add rpcexplorer to webapp hierarchy.

web/inc/rpcexplorer/rpc-descriptor-util.html

 <!--
   Copyright 2016 The LUCI Authors. All rights reserved.
   Use of this source code is governed under the Apache License, Version 2.0
   that can be found in the LICENSE file.
-  -->
+-->
 
 <!--
   rpcExplorer.descUtil exposes helper methods to work with protobuf
   descriptor messages.
   Primarily it implements name and comments resolution in a FileDescriptorSet.
 -->
 <script>
   'use strict';
 
   var rpcExplorer = (function(rpcExplorer) {
@@ skipping 242 matching lines @@
           }
         }
 
         return comment;
       }
     };
 
     return rpcExplorer;
   }(rpcExplorer || {}));
 </script>