debugger: call this.resume() after this.run()

When the debugger has started we need to call `this.resume` otherwise,
the prompt won't appear.

Fixes: nodejs#9854
PR-URL: nodejs#10099
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Rich Trott <rtrott@gmail.com>

lib/_debugger.js

@@ -839,7 +839,7 @@ function Interface(stdin, stdout, args) {
   // Run script automatically
   this.pause();
 
-  setImmediate(() => { this.run(); });
+  setImmediate(() => { this.run(() => this.resume()); });
 }
 
 

test/parallel/test-debug-prompt.js

@@ -0,0 +1,13 @@
+'use strict';
+
+const assert = require('assert');
+const common = require('../common');
+const spawn = require('child_process').spawn;
+
+const proc = spawn(process.execPath, ['debug', 'foo']);
+proc.stdout.setEncoding('utf8');
+
+proc.stdout.once('data', common.mustCall((data) => {
+  assert.strictEqual(data, 'debug> ');
+  proc.kill();
+}));