[JS BE] add tests for es6-classes

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

@@ -0,0 +1,19 @@
+// EXPECTED_REACHABLE_NODES: 1343
+abstract class A {
+    abstract fun foo(): String
+
+    val ss = foo() + "K"
+}
+
+class O(val s: String) {
+    inner class I() : A() {
+        override fun foo() = s
+    }
+
+    fun result() = I().ss
+}
+
+fun box(): String {
+    val o = O("O")
+    return o.result()
+}