Revert "Merge more Kernel infrastructure from kernel_sdk SDK fork."

runtime/lib/null_patch.dart

Index: runtime/lib/null_patch.dart
diff --git a/runtime/lib/null_patch.dart b/runtime/lib/null_patch.dart
index 0f22e67e5679cee1de70115a6f6426f50d87f68e..312804e6b84c9dbb8e47654d25fc6f2ccbf62dd3 100644
--- a/runtime/lib/null_patch.dart
+++ b/runtime/lib/null_patch.dart
@@ -5,7 +5,14 @@
 // Dart core library.
 
 @patch class Null {
+
+  factory Null._uninstantiable() {
+    throw new UnsupportedError("class Null cannot be instantiated");
+  }
+
   static const _HASH_CODE = 2011; // The year Dart was announced and a prime.
   int get hashCode => _HASH_CODE;
   int get _identityHashCode => _HASH_CODE;
+
+  String toString() => 'null';
 }