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

runtime/vm/isolate_test.cc

Index: runtime/vm/isolate_test.cc
diff --git a/runtime/vm/isolate_test.cc b/runtime/vm/isolate_test.cc
index b58dd3d97970dd91022d1a46d43f60e568403fe5..7621a12b8a122cccbc7aa9d9e922c0e32172fd4c 100644
--- a/runtime/vm/isolate_test.cc
+++ b/runtime/vm/isolate_test.cc
@@ -24,6 +24,7 @@ UNIT_TEST_CASE(IsolateCurrent) {
 // not loaded into the isolate).
 TEST_CASE(IsolateSpawn) {
   const char* kScriptChars =
+      "#import('dart:isolate');\n"
       "class SpawnNewIsolate extends Isolate {\n"
       "  SpawnNewIsolate() : super() { }\n"
       "  void main() {\n"