Allow setting alternative debugger frontend path in development

Summary:
Changelog: [Internal]

TSIA

Reviewed By: huntie

Differential Revision: D55074090

packages/debugger-frontend/index.js

@@ -10,6 +10,27 @@
 
 const path = require('path');
 
-const frontEndPath = path.join(__dirname, 'dist', 'third-party', 'front_end');
+let frontEndPath = path.join(__dirname, 'dist', 'third-party', 'front_end');
+
+if (process.env.REACT_NATIVE_DEBUGGER_FRONTEND_PATH != null) {
+  frontEndPath = process.env.REACT_NATIVE_DEBUGGER_FRONTEND_PATH;
+  const ANSI_YELLOW = '\x1b[33m';
+  const ANSI_GREY = '\x1b[90m';
+  const ANSI_WHITE = '\x1b[37m';
+  const ANSI_RESET = '\x1b[0m';
+  console.warn(
+    '\n' +
+      ANSI_YELLOW +
+      'Using custom debugger frontend path from ' +
+      ANSI_WHITE +
+      'process.env.REACT_NATIVE_DEBUGGER_FRONTEND_PATH' +
+      ANSI_YELLOW +
+      ': ' +
+      ANSI_GREY +
+      frontEndPath +
+      ANSI_RESET +
+      '\n',
+  );
+}
 
 module.exports = (frontEndPath /*: string */);