Rename RuntimeError to CyclicIntializationError, as per spec.

runtime/tests/vm/dart/isolate_unhandled_exception_uri_helper.dart

Index: runtime/tests/vm/dart/isolate_unhandled_exception_uri_helper.dart
diff --git a/runtime/tests/vm/dart/isolate_unhandled_exception_uri_helper.dart b/runtime/tests/vm/dart/isolate_unhandled_exception_uri_helper.dart
index a994f1309f4199534ec66a4020b0dcb9a46ff092..b8088a8ee167cf2caf1736be1565089508242ec9 100644
--- a/runtime/tests/vm/dart/isolate_unhandled_exception_uri_helper.dart
+++ b/runtime/tests/vm/dart/isolate_unhandled_exception_uri_helper.dart
@@ -13,7 +13,7 @@ void main() {
   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();