Make dart:collection strong-mode clean.

tests/corelib/set_test.dart

Index: tests/corelib/set_test.dart
diff --git a/tests/corelib/set_test.dart b/tests/corelib/set_test.dart
index 20a136ad6abc6beae5a11f97c11d8d28219eb35d..55e7250aa99b76acc296a0933df0459fd8d2fe88 100644
--- a/tests/corelib/set_test.dart
+++ b/tests/corelib/set_test.dart
@@ -523,5 +523,5 @@ main() {
   testASetFrom((x) => new Set<A>.from(x));
   testASetFrom((x) => new HashSet<A>.from(x));
   testASetFrom((x) => new LinkedHashSet<A>.from(x));
-  testASetFrom((x) => new SplayTreeSet<A>.from(x));
+  testASetFrom((x) => new SplayTreeSet<A>.from(x, identityCompare));
 }