JS: Add test with class stored in global variable

javascript/ql/test/library-tests/DOM/Customizations.expected

@@ -4,3 +4,9 @@ test_locationRef
 | customization.js:3:3:3:14 | doc.location |
 test_domValueRef
 | customization.js:4:3:4:28 | doc.get ... 'test') |
+| tst.js:45:8:45:7 | this |
+| tst.js:46:7:46:12 | this.x |
+| tst.js:49:3:49:8 | window |
+| tst.js:50:3:50:8 | window |
+| tst.js:50:3:50:14 | window.myApp |
+| tst.js:50:3:50:18 | window.myApp.foo |

javascript/ql/test/library-tests/DOM/externs/externs.js

@@ -0,0 +1,10 @@
+/** @externs */
+
+/**
+ * @constructor
+ * @name EventTarget
+ */
+function EventTarget() {}
+
+/** @type {EventTarget} */
+var window;

javascript/ql/test/library-tests/DOM/tst.js

@@ -39,3 +39,13 @@
     factory2();
 
 })();
+
+(function pollute() {
+  class C {
+    foo() {
+      this.x; // Should not be a domValueRef
+    }
+  }
+  window.myApp = new C();
+  window.myApp.foo();
+})();