Implement work-around for "Placeholder for" error in JS output.

tests/lib/lib.status

Index: tests/lib/lib.status
diff --git a/tests/lib/lib.status b/tests/lib/lib.status
index de8f2e4857dd89ddd79a3f81780d88d973461750..e22d31f305f4edc2c7e4b910cda62a043e0482ad 100644
--- a/tests/lib/lib.status
+++ b/tests/lib/lib.status
@@ -155,6 +155,8 @@ json/json_test: Fail                            # Issue 10961
 [ $compiler == dart2js && $minified ]
 mirrors/typedef_test/01: Fail # http://dartbug.com/6490
 mirrors/list_constructor_test/none: Fail # http://dartbug.com/15555
+mirrors/mirrors_used_get_name_test: RuntimeError
+mirrors/mirrors_used_get_name2_test: RuntimeError
 
 [ $runtime == ff ]
 # FF setTimeout can fire early: https://bugzilla.mozilla.org/show_bug.cgi?id=291386