[NI] Render DefinitelyNotNull types with !! postfix

core/descriptors/src/org/jetbrains/kotlin/renderer/DescriptorRendererImpl.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2016 JetBrains s.r.o.
+ * Copyright 2010-2017 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -250,6 +250,10 @@ internal class DescriptorRendererImpl(
         if (type.isMarkedNullable) {
             append("?")
         }
+
+        if (type.isDefinitelyNotNullType) {
+            append("!!")
+        }
     }
 
     private fun StringBuilder.renderTypeConstructorAndArguments(