Rework standalone to use a synchronous loader that does not invoke Dart code

sdk/lib/vmservice/vmservice.dart

Index: sdk/lib/vmservice/vmservice.dart
diff --git a/sdk/lib/vmservice/vmservice.dart b/sdk/lib/vmservice/vmservice.dart
index 445f5d5302d96bc40747da0fe0b881e936dc18d7..dba955574f41233aa483a53907e1c15267aa46f6 100644
--- a/sdk/lib/vmservice/vmservice.dart
+++ b/sdk/lib/vmservice/vmservice.dart
@@ -21,6 +21,10 @@ part 'message_router.dart';
 final RawReceivePort isolateLifecyclePort = new RawReceivePort();
 final RawReceivePort scriptLoadPort = new RawReceivePort();
 
+// This is for use by the embedder. It is a map from the isolateId to
+// anything. When an isolate goes away, it will be removed from this map.
+final Map<int, dynamic> isolateEmbedderData = new Map<int, dynamic>();
+
 // These must be kept in sync with the declarations in vm/json_stream.h.
 const kInvalidParams = -32602;
 const kInternalError = -32603;
@@ -124,6 +128,7 @@ class VMService extends MessageRouter {
       break;
       case Constants.ISOLATE_SHUTDOWN_MESSAGE_ID:
         runningIsolates.isolateShutdown(portId, sp);
+        isolateEmbedderData.remove(portId);
       break;
     }
   }