isolates refactor: this change introduces 'dart:isolate' as a library. This is a

runtime/vm/snapshot_test.cc

Index: runtime/vm/snapshot_test.cc
diff --git a/runtime/vm/snapshot_test.cc b/runtime/vm/snapshot_test.cc
index 22886d3a70c7cb4d537f20cdb6bab6fbbc7d7eb5..58e46854b097b9bbae6aa232b8a866239e0e47b5 100644
--- a/runtime/vm/snapshot_test.cc
+++ b/runtime/vm/snapshot_test.cc
@@ -1468,6 +1468,7 @@ UNIT_TEST_CASE(PostCObject) {
   // Create a native port for posting from C to Dart
   TestIsolateScope __test_isolate__;
   const char* kScriptChars =
+      "#import('dart:isolate');\n"
       "void main() {\n"
       "  var messageCount = 0;\n"
       "  var exception = '';\n"