JS: add test with closures

javascript/ql/test/library-tests/TaintTracking/BasicTaintTracking.expected

@@ -14,6 +14,8 @@
 | promise.js:5:25:5:32 | source() | promise.js:5:8:5:33 | bluebir ... urce()) |
 | sanitizer-guards.js:2:11:2:18 | source() | sanitizer-guards.js:4:8:4:8 | x |
 | sanitizer-guards.js:13:14:13:21 | source() | sanitizer-guards.js:15:10:15:15 | this.x |
+| sanitizer-guards.js:13:14:13:21 | source() | sanitizer-guards.js:21:14:21:19 | this.x |
+| sanitizer-guards.js:13:14:13:21 | source() | sanitizer-guards.js:26:9:26:14 | this.x |
 | thisAssignments.js:4:17:4:24 | source() | thisAssignments.js:5:10:5:18 | obj.field |
 | thisAssignments.js:7:19:7:26 | source() | thisAssignments.js:8:10:8:20 | this.field2 |
 | tst.js:2:13:2:20 | source() | tst.js:4:10:4:10 | x |

javascript/ql/test/library-tests/TaintTracking/sanitizer-guards.js

@@ -16,6 +16,14 @@ class C {
 
     if (isSafe(this.x)) {
       sink(this.x); // OK
+
+      addEventListener('hey', () => {
+        sink(this.x); // OK - but still flagged
+      });
     }
+
+    addEventListener('hey', () => {
+	  sink(this.x); // NOT OK
+	});
   }
 }