isolates: remove Isolate2 interface, add top-level spawn functions, more comments

runtime/lib/isolate.dart

Index: runtime/lib/isolate.dart
diff --git a/runtime/lib/isolate.dart b/runtime/lib/isolate.dart
index e91fd0ea416acadc15eaca9405d2b52c8e0df7c2..5974946110df22ffe278727c2cc87fa77698106c 100644
--- a/runtime/lib/isolate.dart
+++ b/runtime/lib/isolate.dart
@@ -155,13 +155,14 @@ class _IsolateNatives {
       native "IsolateNatives_start";
 }
 
-class _IsolateFactory {
+// TODO(sigmund,turnidge): implement
 
-  factory Isolate2.fromCode(Function topLevelFunction) {
-    throw new NotImplementedException();
-  }
+SendPort _spawnFunction(void topLevelFunction()) {
+  throw new NotImplementedException();
+}
 
-  factory Isolate2.fromUri(String uri) {
-    throw new NotImplementedException();
-  }
+SendPort _spawnUri(String uri) {
+  throw new NotImplementedException();
 }
+
+ReceivePort _port = null;