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

lib/isolate/isolate_compiler.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 
 // Dart isolate's API for the dartc compiler (only used for type checking in the
 // dart editor, but not for code generation).
 #library("dart:isolate");
 
 #source("isolate_api.dart");
 
-class _IsolateFactory {
+SendPort _spawnFunction(void topLevelFunction()) {
+  throw new NotImplementedException();
+}
 
-  factory Isolate2.fromCode(Function topLevelFunction) {
-    throw new NotImplementedException();
-  }
-
-  factory Isolate2.fromUri(String uri) {
-    throw new NotImplementedException();
-  }
+SendPort _spawnUri(String uri) {
+  throw new NotImplementedException();
 }
 
 class _IsolateNatives {
   static Future<SendPort> spawn(Isolate isolate, bool isLight) {
     throw new NotImplementedException();
   }
 }
 
 class _ReceivePortFactory {
 
   factory ReceivePort() {
     throw new NotImplementedException();
   }
 
   factory ReceivePort.singleShot() {
     throw new NotImplementedException();
   }
 }