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

runtime/lib/isolate.dart

Index: runtime/lib/isolate.dart
diff --git a/runtime/lib/isolate.dart b/runtime/lib/isolate.dart
index 13ec8dd66cd9f39bfcfb6878fbeea9f35e76e278..22ddca07a38f588ec052ee51e3d7081307af4c62 100644
--- a/runtime/lib/isolate.dart
+++ b/runtime/lib/isolate.dart
@@ -139,8 +139,7 @@ class SendPortImpl implements SendPort {
   final int _id;
 }
 
-
-class IsolateNatives {
+class _IsolateNatives {
   static Future<SendPort> spawn(Isolate isolate, bool isLight) {
     Completer<SendPort> completer = new Completer<SendPort>();
     SendPort port = _start(isolate, isLight);
@@ -155,3 +154,14 @@ class IsolateNatives {
   static SendPort _start(Isolate isolate, bool light)
       native "IsolateNatives_start";
 }
+
+class _IsolateFactory {
+
+  factory Isolate2.fromCode(Function topLevelFunction) {
+    throw new NotImplementedException();
+  }
+
+  factory Isolate2.fromUri(String uri) {
+    throw new NotImplementedException();
+  }
+}