Skip mirrors_reader_test on mobile safari.

tests/lib/lib.status

Index: tests/lib/lib.status
diff --git a/tests/lib/lib.status b/tests/lib/lib.status
index 0ccee40589c14eed5f9501bbe04aac2db1193739..cd114fabbdfcff1b145b2ffb1682d7fd2752fc30 100644
--- a/tests/lib/lib.status
+++ b/tests/lib/lib.status
@@ -280,6 +280,9 @@ convert/streamed_conversion_utf8_decode_test: Skip # Times out or passes. Issue
 mirrors/lazy_static_test: Skip # Times out. Issue 19127
 mirrors/mirrors_reader_test: Skip # Times out. Issue 19127
 
+[ $compiler == dart2js && $runtime == safarimobilesim ]
+mirrors/mirrors_reader_test: Skip # Times out. Issue 20806.
+
 [ $compiler == dart2dart ]
 # Deferred loading is not supported by dart2dart.
 async/deferred/deferred_in_isolate_test: Skip # Issue 17523