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

runtime/vm/bootstrap_nocorelib.cc

Index: runtime/vm/bootstrap_nocorelib.cc
diff --git a/runtime/vm/bootstrap_nocorelib.cc b/runtime/vm/bootstrap_nocorelib.cc
index 1905ee48ed6af532f8cbfc8e110df0c7b558f0ff..09ceba45da2298a663f0bed2480b08ef1bd35c5b 100644
--- a/runtime/vm/bootstrap_nocorelib.cc
+++ b/runtime/vm/bootstrap_nocorelib.cc
@@ -26,6 +26,10 @@ RawScript* Bootstrap::LoadImplScript() {
   return Script::null();
 }
 
+RawError* Bootstrap::InitAdditionalLibraries() {
+  UNREACHABLE();
+  return Error::null();
+}
 
 RawError* Bootstrap::Compile(const Library& library, const Script& script) {
   UNREACHABLE();