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..db6e8012ac6340975363d0b0e580be762bf07375 100644
--- a/runtime/vm/bootstrap_nocorelib.cc
+++ b/runtime/vm/bootstrap_nocorelib.cc
@@ -27,6 +27,12 @@ RawScript* Bootstrap::LoadImplScript() {
 }
 
 
+RawScript* Bootstrap::LoadIsolateScript() {
+  UNREACHABLE();
+  return Script::null();
+}
+
+
 RawError* Bootstrap::Compile(const Library& library, const Script& script) {
   UNREACHABLE();
   return Error::null();