JS IR: support kotlin.test

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/ir/descriptorBasedUtils.kt

@@ -0,0 +1,11 @@
+/*
+ * Copyright 2010-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.backend.common.ir
+
+import org.jetbrains.kotlin.descriptors.MemberDescriptor
+import org.jetbrains.kotlin.ir.declarations.IrDeclaration
+
+val IrDeclaration.isExpect get() = descriptor.let { it is MemberDescriptor && it.isExpect }