Rename RuntimeError to CyclicIntializationError, as per spec.

runtime/tests/vm/dart/isolate_unhandled_exception_test2.dart

Index: runtime/tests/vm/dart/isolate_unhandled_exception_test2.dart
diff --git a/runtime/tests/vm/dart/isolate_unhandled_exception_test2.dart b/runtime/tests/vm/dart/isolate_unhandled_exception_test2.dart
index 6fc0a1113d786acda8d7952a23d0c30b0c2069a7..7fe1c86de2da4fee1c54731dc75ae956e369bc07 100644
--- a/runtime/tests/vm/dart/isolate_unhandled_exception_test2.dart
+++ b/runtime/tests/vm/dart/isolate_unhandled_exception_test2.dart
@@ -19,7 +19,7 @@ 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();