dart2js CPS: implement special handling of the Symbol constructor.

tests/lib/lib.status

Index: tests/lib/lib.status
diff --git a/tests/lib/lib.status b/tests/lib/lib.status
index f5d5af221b2803bfd1f1eb8431e957d024984519..d854ac9c2c0f8c97b9765a0601f12afb4185ea0e 100644
--- a/tests/lib/lib.status
+++ b/tests/lib/lib.status
@@ -338,7 +338,6 @@ convert/streamed_conversion_json_utf8_decode_test: Skip  # Timeout.
 async/async_await_zones_test: Crash # (await for(var x in bar().take(100)){sum+= x;}): await for
 async/stream_iterator_test: Crash # (Stream createCancel...  cannot handle sync*/async* functions
 mirrors/parameter_annotation_mirror_test: Pass, Fail # Issue 25501.  Depends on inlining.
-mirrors/symbol_validation_test/none: RuntimeError # Please triage this failure.
 
 [ $compiler == dart2js && $cps_ir && $host_checked ]
 mirrors/circular_factory_redirection_test/02: Crash # Assertion failure: Constant constructor already computed for generative_constructor(A#circular2)