Add proper API for creating private symbols wrt a library.

pkg/pkg.status

Index: pkg/pkg.status
diff --git a/pkg/pkg.status b/pkg/pkg.status
index 5714c0a0d182d2f0c97ba46ba67d30fc0794c2fb..ca46ff9f0987e7bfe4629b98bc8dd5d3680100fc 100644
--- a/pkg/pkg.status
+++ b/pkg/pkg.status
@@ -206,6 +206,7 @@ unittest/test/*_minified_test: Skip # DO NOT COPY THIS UNLESS YOU WORK ON DART2J
 # test on Dartium, which requires all tests to have a library.
 [ $compiler == none && ( $runtime == dartium || $runtime == drt ) ]
 serialization/test/no_library_test: Skip # Expected Failure
+serialization/test/serialization_test: Fail # Issue 13598
 
 # Skip tests on the VM if the package depends on dart:html
 [ $runtime == vm ]
@@ -214,6 +215,7 @@ mdv: Skip
 mutation_observer: Skip
 polymer_expressions/test/syntax_test: Skip
 third_party/html5lib/test/browser/browser_test: Skip
+serialization/test/serialization_test: Fail # Issue 13598
 
 [ $runtime == safari || $runtime == chrome || $runtime == ie9 || $runtime == ff || $runtime == dartium || $runtime == drt ]
 docgen/test/single_library_test: Skip # Uses dart:io