Fix the return type of String.split in DDC to be correct

tests/corelib_2/corelib_2.status

Index: tests/corelib_2/corelib_2.status
diff --git a/tests/corelib_2/corelib_2.status b/tests/corelib_2/corelib_2.status
index 70e590256f4d212edcc494c1e69ebf3173da200a..8d0753c5e6b6efdffa8af87c7ba89be2bf9948f8 100644
--- a/tests/corelib_2/corelib_2.status
+++ b/tests/corelib_2/corelib_2.status
@@ -181,6 +181,7 @@ integer_to_string_test/01: RuntimeError
 iterable_to_set_test: RuntimeError # is-checks do not implement strong mode type system
 int_parse_radix_test/01: RuntimeError
 int_parse_radix_test/02: RuntimeError

[Leaf, 2017/08/24 17:30:09]

File a bug for these?

+string_split_test: RuntimeError # does not return List<String>
 
 [ $compiler == dart2js && $runtime == drt && $csp && $minified ]
 core_runtime_types_test: Pass, Fail # Issue 27913
@@ -461,6 +462,9 @@ stopwatch_test: Skip  # Flaky test due to expected performance behaviour.
 [ $runtime == vm ]
 string_case_test/01: RuntimeError
 
+[ $runtime == vm || $runtime == dart_precompiled ]
+string_split_test: RuntimeError # does not return List<String>
+
 [ $compiler == dart2js && $dart2js_with_kernel && $host_checked ]
 apply2_test: Crash
 apply3_test: Crash