[JS BE] add tests for es6-classes

js/js.translator/testData/box/es6classes/inheritedFromExternalBySecondaryCtor.kt

@@ -0,0 +1,19 @@
+//IGNORE_BACKEND: JS, JS_IR
+
+open external class E(x: Int, y: Int) {
+    val t: Int = definedExternally
+}
+
+open class A(i: Int, j: Int) : E(i, j)
+
+class B : A {
+    constructor() : super(3, 4)
+}
+
+fun box(): String {
+    val b = B()
+
+    assertEquals(7, b.t)
+
+    return "OK"
+}