assert: lazy load acorn

This makes sure acorn is only loaded in case it is necessary.

PR-URL: #19863
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/assert.js

@@ -33,7 +33,6 @@ const {
   }
 } = require('internal/errors');
 const { openSync, closeSync, readSync } = require('fs');
-const { parseExpressionAt } = require('internal/deps/acorn/dist/acorn');
 const { inspect } = require('util');
 const { EOL } = require('os');
 const { NativeModule } = require('internal/bootstrap/loaders');
@@ -173,6 +172,8 @@ function getErrMessage(call) {
     fd = openSync(filename, 'r', 0o666);
     const buffers = getBuffer(fd, line);
     const code = Buffer.concat(buffers).toString('utf8');
+    // Lazy load acorn.
+    const { parseExpressionAt } = require('internal/deps/acorn/dist/acorn');
     const nodes = parseExpressionAt(code, column);
     // Node type should be "CallExpression" and some times
     // "SequenceExpression".