First set of test triage for fast-startup

tests/lib/lib.status

Index: tests/lib/lib.status
diff --git a/tests/lib/lib.status b/tests/lib/lib.status
index b280b4f4c4f9017b8bbe8d53578db3666b7f50ac..b74f509a8f5e7b9d52692d9167348431898ac97e 100644
--- a/tests/lib/lib.status
+++ b/tests/lib/lib.status
@@ -104,6 +104,9 @@ mirrors/raw_type_test/01: RuntimeError # Issue 6490
 mirrors/mirrors_reader_test: Slow, RuntimeError # Issue 16589
 mirrors/regress_26187_test: RuntimeError # Issue 6490
 
+[ $compiler == dart2js && $fast_startup ]
+mirrors/*: Fail # mirrors not supported
+
 [ $runtime == safari || $runtime == safarimobilesim ]
 typed_data/int32x4_test: Fail, Pass # Safari has an optimization bug (nightlies are already fine).
 typed_data/float32x4_test: Fail, Pass # Safari has an optimization bug (nightlies are already fine).