Rename RuntimeError to CyclicIntializationError, as per spec.

runtime/tests/vm/dart/isolate_unhandled_exception_test.dart

Index: runtime/tests/vm/dart/isolate_unhandled_exception_test.dart
diff --git a/runtime/tests/vm/dart/isolate_unhandled_exception_test.dart b/runtime/tests/vm/dart/isolate_unhandled_exception_test.dart
index f7b0c04e910d3dcec5e15d7d36562f98f6e2fd1b..798221e190ddb47f55537761b05bdef71185bd24 100644
--- a/runtime/tests/vm/dart/isolate_unhandled_exception_test.dart
+++ b/runtime/tests/vm/dart/isolate_unhandled_exception_test.dart
@@ -21,7 +21,7 @@ void entry() {
   port.receive((message, replyTo) {
     if (message == 'throw exception') {
       replyTo.call('throwing exception');
-      throw new RuntimeError('ignore this exception');
+      throw new UnsupportedError('ignore this exception');
     }
     replyTo.call('hello');
     port.close();