Make dart2js code retain the original stack trace for uncaught async errors.

tests/lib/lib.status

Index: tests/lib/lib.status
diff --git a/tests/lib/lib.status b/tests/lib/lib.status
index 57f42c490595dac434ec8220bcba0a3234db95c7..2c983c3b86f8ae159d1266935be4384ae9312f7a 100644
--- a/tests/lib/lib.status
+++ b/tests/lib/lib.status
@@ -359,6 +359,9 @@ mirrors/mirrors_used_typedef_declaration_test/01: Crash # Assertion failure: typ
 mirrors/mirrors_used_typedef_declaration_test/none: Crash # Assertion failure: typedef(Foo) has not been checked for cycles.
 mirrors/typedef_library_test: Crash # Assertion failure: typedef(G) has not been checked for cycles.
 
+[ $compiler != dart2js ]
+async/dart2js_uncaught_error_test: Skip  # JS-integration only test
+
 [ $noopt ]
 mirrors/*: SkipByDesign
 convert/chunked_conversion_utf88_test: Pass, Timeout