Automatically remove testing code when ejecting.

Author: bnjmnt4n

packages/react-scripts/scripts/start.js

@@ -41,8 +41,8 @@ var DEFAULT_PORT = process.env.PORT || 3000;
 var compiler;
 var handleCompile;
 
-// You can safely remove this after ejecting.
-// We only use this block for testing of Create React App itself:
+// @remove-on-eject-begin
+// This block is used for testing of Create React App itself:
 var isSmokeTest = process.argv.some(arg => arg.indexOf('--smoke-test') > -1);
 if (isSmokeTest) {
   handleCompile = function (err, stats) {
@@ -53,6 +53,7 @@ if (isSmokeTest) {
     }
   };
 }
+// @remove-on-eject-end
 
 function setupCompiler(host, port, protocol) {
   // "Compiler" is a low-level interface to Webpack.