Add a library for manipulating stack traces.

pkg/pkg.status

Index: pkg/pkg.status
diff --git a/pkg/pkg.status b/pkg/pkg.status
index b90eaa19958a90e574ca6296a30a8ea9e3a1dbb7..e96bd26a673a52c3e8363ce8119864ae15116ed0 100644
--- a/pkg/pkg.status
+++ b/pkg/pkg.status
@@ -37,6 +37,11 @@ pathos/test/*: Skip
 # Issue 8440 forces us to use pathos in the scheduled_test tests, which would
 # otherwise be dart2js-compatible.
 scheduled_test/test/*: Skip
+
+# We use pathos in the stack_trace tests. We can run them on dart2js when issue
+# 6943 is fixed.
+stack_trace/test/*: Skip
+
 source_maps/test/vlq_test: Fail # A VLQ test checks for large numbers that
                                 # overflow in JS (numbers slightly larger than
                                 # 32 bits where we do bitwise operations).