Add proper API for creating private symbols wrt a library.

tests/lib/lib.status

Index: tests/lib/lib.status
diff --git a/tests/lib/lib.status b/tests/lib/lib.status
index 8928dadb426766be50994fa5f89670eff54503dd..8822a07c1782cd28dd07b2de924bdbd3adb6ba3a 100644
--- a/tests/lib/lib.status
+++ b/tests/lib/lib.status
@@ -43,6 +43,9 @@ mirrors/typedef_test/none: RuntimeError # http://dartbug.com/6490
 mirrors/redirecting_factory_test/none: RuntimeError # Issue 6490
 mirrors/redirecting_factory_test/02: RuntimeError # Issue 6490
 mirrors/closures_test/none: RuntimeError # Issue 6490
+mirrors/symbol_validation_test: RuntimeError # Issue 13597
+mirrors/private_symbol_test: CompileTimeError # Issue 13597
+
 
 [ $runtime == safari ]
 mirrors/return_type_test: Pass, Timeout # Issue 12858
@@ -136,6 +139,7 @@ mirrors/redirecting_factory_test/none: Fail # Issue 13365
 mirrors/redirecting_factory_test/01: Fail # Issue 13365
 mirrors/redirecting_factory_test/02: Fail # Issue 13365
 mirrors/closures_test/01: Fail, OK # Incorrect dart2js behavior.
+mirrors/symbol_validation_test: RuntimeError # Issue 13596
 
 [ $compiler == none && $runtime == drt ]
 async/timer_isolate_test: Skip # See Issue 4997