Make dart2js Isolate.spawn work.

sdk/lib/_internal/lib/isolate_patch.dart

Index: sdk/lib/_internal/lib/isolate_patch.dart
diff --git a/sdk/lib/_internal/lib/isolate_patch.dart b/sdk/lib/_internal/lib/isolate_patch.dart
index 4f9ac711fbff3707dfce71c6cd8f20ff19ef1221..397b408b1e106cd004a96d84944c25975d61fd4d 100644
--- a/sdk/lib/_internal/lib/isolate_patch.dart
+++ b/sdk/lib/_internal/lib/isolate_patch.dart
@@ -12,10 +12,11 @@ import 'dart:_isolate_helper' show IsolateNatives,
 
 patch class Isolate {
   patch static Future<Isolate> spawn(void entryPoint(message), var message) {
-    throw new UnimplementedError("spawn");
+    SendPort controlPort = IsolateNatives.spawnFunction(entryPoint, message);
+    return new Future<Isolate>.value(new Isolate._fromControlPort(controlPort));
   }
 
-  patch static Future<Isolate> spawnUri(Uri uri, var arguments) {
+  patch static Future<Isolate> spawnUri(Uri uri, var message) {
     throw new UnimplementedError("spawn uri");
   }
 }
@@ -28,18 +29,8 @@ patch class _Isolate {
     return lazyPort;
   }
 
-  static SendPort _spawnFunction(void topLevelFunction(),
-      [bool unhandledExceptionCallback(IsolateUnhandledException e)]) {
-    if (unhandledExceptionCallback != null) {
-      // TODO(9012): Implement the UnhandledExceptionCallback.
-      throw new UnimplementedError(
-          "spawnFunction with unhandledExceptionCallback");
-    }
-    return IsolateNatives.spawnFunction(topLevelFunction);
-  }
-
   patch static SendPort spawnUri(String uri) {
-    return IsolateNatives.spawn(null, uri, false);
+    return IsolateNatives.spawn(null, uri, null, false);
   }
 }
 
@@ -58,4 +49,4 @@ patch class RawReceivePort {
   patch factory RawReceivePort([void handler(event)]) {
     throw new UnimplementedError("RawReceivePort");
   }
-}
+}