Moved frontend overrides out of front-end folder

Moved front-end/node/Overrides.js out of front-end folder, so that it is
easier to pull new versions of front-end from Blink DevTools.

lib/debug-server.js

@@ -13,6 +13,10 @@ function debugAction(req, res) {
   res.sendfile(path.join(WEBROOT, 'inspector.html'));
 }
 
+function overridesAction(req, res) {
+  res.sendfile(path.join(__dirname, '../front-end-node/Overrides.js'));
+}
+
 function getDebuggerPort(url, defaultPort) {
   return parseInt((/\?port=(\d+)/.exec(url) || [null, defaultPort])[1], 10);
 }
@@ -43,6 +47,7 @@ DebugServer.prototype.start = function(options) {
   var httpServer = http.createServer(app);
 
   app.get('/debug', debugAction);
+  app.get('/node/Overrides.js', overridesAction);
   app.use(express.static(WEBROOT));
 
   var ws = io.listen(httpServer);