JS backend: fix is for trait. #KT-3519 fixed

js/js.translator/testFiles/rtti/cases/rttiForTrait.kt

@@ -0,0 +1,20 @@
+package foo
+
+
+open class A
+
+trait B
+
+class C: A(), B
+
+fun box(): String {
+
+    val a = A()
+    val b = object : B {}
+    val c = C()
+
+    if (a is B) return "a is B"
+    if (b !is B) return "b !is B"
+    if (c !is B) return "c !is B"
+    return "OK"
+}

js/js.translator/testFiles/rtti/cases/rttiForTrait2.kt

@@ -0,0 +1,36 @@
+package foo
+
+trait A
+trait B : A
+trait C : A
+trait D : B, C
+trait E : C
+
+open class CB: B
+class CB2: CB()
+
+class CD: D
+
+fun testPhrase(o: Any): String {
+    var s = ""
+    s += if(o is A) "Y" else "N"
+    s += if(o is B) "Y" else "N"
+    s += if(o is C) "Y" else "N"
+    s += if(o is D) "Y" else "N"
+    s += if(o is E) "Y" else "N"
+    return s
+}
+
+fun box(): String {
+    val b = CB()
+    val b2 = CB2()
+    val d = CD()
+    val e = object : E {}
+
+    if (testPhrase(b) != "YYNNN") return "bad b, it: ${testPhrase(b)}"
+    if (testPhrase(b2) != "YYNNN") return "bad b2, it: ${testPhrase(b2)}"
+    if (testPhrase(d) != "YYYYN") return "bad d, it: ${testPhrase(d)}"
+    if (testPhrase(e) != "YNYNY") return "bad e, it: ${testPhrase(e)}"
+
+    return "OK"
+}