Mark uri_parse_test slow on ddc

This is something we'll want to investigate. It looks like dartdevk's
performance using its own SDK is slightly worse, suggesting it's missing
some optimizations (e.g. `JS` types that are not recognized, extra null
checks, covariance check elimination).

Change-Id: Ieaedd6be3bfb70718f495fc86cb1adcf67aad3cc
Reviewed-on: https://dart-review.googlesource.com/59580
Reviewed-by: Jenny Messerly <jmesserly@google.com>
diff --git a/tests/corelib_2/corelib_2.status b/tests/corelib_2/corelib_2.status
index 069a2f2..a6970b9 100644
--- a/tests/corelib_2/corelib_2.status
+++ b/tests/corelib_2/corelib_2.status
@@ -466,6 +466,7 @@
 symbol_reserved_word_test/12: RuntimeError # Issue 29921
 symbol_test/none: RuntimeError # Issue 29921
 typed_data_with_limited_ints_test: Skip # Requires fixed-size int64 support.
+uri_parse_test: Pass, Slow
 
 [ $runtime == vm && !$strong ]
 collection_of_test: RuntimeError