Merge branch 'fix-webpack-dev-server-proxy' into 'master'

Fix webpack dev server when behind proxy

See merge request !9543

lib/gitlab/middleware/webpack_proxy.rb

@@ -8,16 +8,16 @@ module Gitlab
         @proxy_host = opts.fetch(:proxy_host, 'localhost')
         @proxy_port = opts.fetch(:proxy_port, 3808)
         @proxy_path = opts[:proxy_path] if opts[:proxy_path]
-        super(app, opts)
+
+        super(app, backend: "http://#{proxy_host}:#{proxy_port}", **opts)
       end
 
       def perform_request(env)
-        unless @proxy_path && env['PATH_INFO'].start_with?("/#{@proxy_path}")
-          return @app.call(env)
+        if @proxy_path && env['PATH_INFO'].start_with?("/#{@proxy_path}")
+          super(env)
+        else
+          @app.call(env)
         end
-
-        env['HTTP_HOST'] = "#{@proxy_host}:#{@proxy_port}"
-        super(env)
       end
     end
   end